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Atomic spectrometry update. X-ray fluorescence spectrometry
Margaret West,*aAndrew T. Ellis,
bPeter Kregsamer,
cPhilip J. Potts,
d
Christina Streli,cChristine Vanhoof
eand Peter Wobrauschek
c
Received 6th August 2007
First published as an Advance Article on the web 3rd September 2007
DOI: 10.1039/b712079f
1 Introduction and reviews
2 Instrumentation
2.1 General instrumentation and excitation sources
2.2 Detectors
3 Spectrum analysis, matrix correction and calibration
procedures
3.1 Spectrum analysis
3.2 Matrix correction and calibration procedures
4 X-ray optics and microfluorescence
5 Synchrotron radiation
5.1 Instrumentation
5.2 Applications
6 TXRF
6.1 Instrumentation
6.2 Synchrotron radiation induced TXRF
6.3 Applications
7 Portable and mobile XRF
8 On-line XRF
9 Applications
9.1 Sampling, sample preparation and pre-concentration
techniques
9.2 Geological and industrial minerals
9.3 Environmental
9.3.1 Atmospheric particulate matter
9.3.2 Other environmental studies
9.4 Archaeological, cultural heritage and forensic
9.5 Industrial
9.6 Clinical and biological
9.7 Thin films and coatings
9.8 Chemical state, speciation and crystal characterisation
10 Abbreviations
11 References
This annual review of X-ray fluorescence covers developments
over the period 2006–2007 in instrumentation and detectors,
matrix correction and spectrum analysis procedures, X-ray
optics and micro-fluorescence, synchrotron XRF, TXRF, porta-
ble XRF and on-line applications as assessed from the published
literature. The review also covers a survey of applications,
including sample preparation, geological, environmental, ar-
chaeological, forensic, biological, clinical, thin films, chemical
state and speciation studies. Interest continues in micro-analy-
tical instrumentation with synchrotron-based systems benefiting
from the availability of more intense beams and efficient focusing
optics. Many authors have strengthened the influence of their
work with data presented as elemental maps and, where appro-
priate, factor analysis continues to feature. In common with
other analytical techniques, this review demonstrates the emer-
ging field of metallomics to assist in the understanding of how
metals and metalloids interact within cells and tissues. Progress
continues to support legislation with further analytical methods
and reference materials available for environmental and indus-
trial applications. Improvements in detector resolution and
excitation optics have helped to strengthen interest in EDXRF
systems to meet the demands from society for a reduction in
pollutants in ambient air. The writing team would welcome
feedback from readers of this review and invite you to com-
plete the Atomic Spectroscopy Updates questionnaire on
www.asureviews.org.
1 Introduction and reviews
This review continues the series of annual Atomic Spectro-
scopy Updates in X-ray Fluorescence Spectrometry1 and
should be read in conjunction with other related reviews in
the series.2–4 In preparing this review, the writing team con-
sidered the wealth of XRF papers published during the period
2006–7. As the XRF technique matures, it is inevitable that
many papers concentrate on applications, with fewer publica-
tions related to instrumentation, spectrum analysis, matrix
correction and calibration procedures. In an attempt to im-
prove the reader’s experience, this review has concentrated on
papers that demonstrated progress in XRF techniques in the
hope of encouraging further developments to assist analytical
endeavours.
The XRF community is now supported by a number of
conferences that offer delegates both oral and poster presenta-
tions along with the opportunity to meet suppliers in an
exhibition forum. The 12th European X-ray Spectrometry
Conference5 was held in June 2006 in Paris, with invited
speakers from ten countries. In August 2006, the 55th Annual
Denver X-ray Conference returned to its Colorado home with
its familiar mix of sessions and workshops for users of both
XRF and XRD. This year the British Crystallography Asso-
ciation celebrated their 25th Annual Spring Meeting6 in
Canterbury with a series of XRF sessions organised by their
Industrial Group.
aWest X-ray Solutions Ltd, 405 Whirlowdale Road, Sheffield, UKS11 9NF
bOxford Instruments Analytical Oy, Nihtisillankuja 5, FI-02630Espoo, Finland
c TU Wien, Atominstitut der Osterreichischen Universitaten,Stadionallee 2, A-1020 Vienna, Austria
d Faculty of Science, The Open University, Walton Hall, MiltonKeynes, UK MK7 6AA
eVITO, Environmental Measurements, Boeretang 200, B-2400 Mol,Belgium
1304 | J. Anal. At. Spectrom., 2007, 22, 1304–1332 This journal is �c The Royal Society of Chemistry 2007
ASU REVIEW www.rsc.org/jaas | Journal of Analytical Atomic Spectrometry
A practical handbook7 with contributions from many
authors from academia and industry provided self-contained
modules featuring XRF instrumentation, quantification meth-
ods and most of the current XRF applications. This book was
designed as a resource for graduate students, research scientist
and industrial readers. Thomsen8 published a timeline of
atomic spectroscopy that provided a short history of the
experimental and theoretical developments for elemental spec-
trochemical analysis. The instrumental techniques included
optical emission (flame, arc/spark, ICP, glow-discharge and
laser ablation), atomic absorption and XRF.
Analytical chemists striving to report reliable results on
elemental mass fractions will be familiar with quality manage-
ment systems and efforts to demonstrate traceability. Padilla
Alvarez led an international group9 on work to demonstrate
traceability and the evaluation of the performance of EDXRF
systems. The authors considered linearity, working range,
precision, trueness and detection limits, with recommenda-
tions for the quantification of uncertainty and the organisation
of internal quality control practices.
2 Instrumentation
2.1 General instrumentation and excitation sources
The range of commercial spectrometers continues to increase
with configurations available to satisfy the demand from both
industry and academia for cost-effective, rapid, non-destruc-
tive quantitative analysis. Energy dispersive X-ray spectro-
meters have gained in popularity in recent years, being
available for laboratory based and in situ applications. How-
ever, it is recognised that the main disadvantages of EDXRF
compared with WDXRF systems are the lower energy resolu-
tion and the count-rate limitation, which lead to reduced
accuracy and precision. Padilla Alvarez and colleagues10 pre-
sented research that combined a compact design for secondary
target excitation in a polarised energy dispersive configuration
with a digital signal processing-based spectrometer. The ar-
rangement was designed to increase the effective solid angles
and to reduce the distances between secondary target, sample
and detector in order to achieve larger X-ray fluxes for both
excitation and detection. The improvement achieved in instru-
mental sensitivity gave better counting statistics and reduced
measuring times to satisfy the authors’ aim of achieving more
accurate and less time-consuming analyses of metal pollutants
in environmental samples and improvements for the determi-
nation of trace elements in archaeological ceramics. The
authors quoted an increase in instrumental sensitivity by a
factor of45 without increasing the dead time above 20%. The
purchase of EDXRF instrumentation requires critical evalua-
tion of a wide range of instrumental features in relation to the
intended application and these were comprehensively covered
in a recent report by the Instrumental Criteria Sub-committee
of the Analytical Methods Committee of the Royal Society of
Chemistry.11 This report may also be useful as a teaching aid.
Wavelength dispersive spectrometry for ‘‘soft’’ X-rays re-
quires monochromators that are efficient in terms of both
luminosity and resolution. Andre et al.12 offered a solution
for wavelengths larger than 3 nm through the use of multi-
layer interference mirrors (MIMs) consisting of a periodic
stack of bilayers with alternating light and heavy materials
on the nano-scale. In 1992, it was proposed that decreasing the
bandwidth of MIMs by etching mirrors with a large number of
bilayers, according to the profile of a lamellar grating, an
improvement in resolution could be obtained. To date, much
progress has been made in the design and fabrication of such
monochromators, enabling the authors to demonstrate an
improvement in resolving power when compared with inter-
ference mirrors. This publication also reported developments
in tunable radiation sources based on the interaction of
medium-energy electron beams with periodic multi-layer
structures.
Dukhanin and Pavlinsky13 compared X-ray tubes with
different anodes and varying beryllium window thicknesses
for the selective excitation of fluorine, oxygen, nitrogen and
carbon. The authors recognised that for these low atomic
number analytes, ionisation of the atoms may occur due to
L-radiation of the matrix arising as a result of intra-atomic
cascade transitions as well as the familiar effects due to
K-radiation or L-radiation of the matrix. Cascade transitions
change primary photons into low-energy photons of the
matrix, which are effective in exciting X-ray fluorescence of
elements with low Z values. Selective excitation effect values
were calculated with consideration of atom excitation by
photo and Auger electrons that originated in the irradiated
sample material.
Moving up the periodic table, Etschmann et al.14 developed
a selective X-ray Bragg spectrometer for an XRF microprobe
for the detection of precious metals in geological and biologi-
cal samples. Their aim was to improve detection limits and
reduce interference from major elements in the sample matrix
and the scattered beam. The configuration used Bragg diffrac-
tion from a surface shaped to a log-spiral to focus X-rays of a
particular energy onto a solid-state detector. The authors
reported enhancement of the precious metal lines within the
relatively narrow bandpass of the Bragg crystal surface and
suppression of sample matrix interference and detector arte-
facts such as tailing and escape peaks. Their efforts were
rewarded with an improvement in the detection limit for Au
in geological samples by an order of magnitude.
2.2 Detectors
In what was generally a sparse year, the number of publica-
tions on pixellated semiconductor detectors stands out and
provides most of the interest from the review year. That said,
most of the work on pixellated detectors is obviously targeted
at imaging applications such as X-ray astronomy or high
energy physics experiments. A silicon CCD employing a
p-channel design on an n-type silicon wafer was described by
Matsuura and co-workers.15 The advantage of the n-type
structure was the high resistivity of the base material and the
depletion depth thickness of 300 mm that could be achieved
compared with the more typical o50 mm active thickness of
conventional CCDs. A 512 by 512 array of 24 by 24 mm2 pixels
was fabricated and when cooled to �110 1C an energy resolu-
tion of 202 eV was obtained at 5.9 keV at a readout frequency
of 67 kHz. The poor effective stopping power for higher
This journal is �c The Royal Society of Chemistry 2007 J. Anal. At. Spectrom., 2007, 22, 1304–1332 | 1305
energy photons (up to 100 keV) of silicon CCDs was addressed
by Miyata et al.,16,17 who directly coupled a scintillating
material to the rear surface of a back-illuminated CCD. Low
energy (o10 keV) X-rays were detected conventionally in the
silicon CCD and high energy ones in the scintillation layer
behind. The scintillation material was needle-like CsI(Tl) and
the high efficiency for visible light of the CCD was valuable
but the energy resolution of the resulting detector was a dismal
6.3 keV at 22.1 keV and 15 keV at 59.5 keV. The detector was
suitable for wide-band X-ray photon counting/imaging in its
intended use in a hard X-ray space telescope, but little else.
Much better stopping power can be obtained using pixels of
materials other than silicon and an array of 1 mm thick CdTe
pixels bump bonded to Medipix readout chips on a 55 mmpitch was studied by Maiorino et al.18 The pixel material and
thickness yielded high detection efficiency for the 122 keV line
from a 57Co radioisotope source. These authors reported in
detail their studies on the critically important charge sharing
effects in such pixellated detectors, which is an issue often
skimmed over but of particular importance for detectors with
larger volume pixels and for high energy photons. The charge
collection characteristics of pnCCDs developed by a team at
MPI Munich were modelled and reported by Kimmel et al.19
Their purely analytical model was able to reconstruct charge
collection parameters for single photon interactions and the
precision of the model data was determined by means of
Monte Carlo simulations and the analysis of experimental
data. An interesting hetero-structure pixellated detector with
high X-ray stopping power was described by Kostamo and co-
workers.20 The novel device comprised a high purity germa-
nium active volume onto which a gallium arsenide layer was
deposited by means of a vertical furnace vapour-phase epitaxy
system. The gallium arsenide layer replaced the typical lithium
diffused n+ contact and the authors concluded that the n+
contact was formed by diffusion of arsenic into the germanium
layer during deposition. The authors claimed that the proces-
sing of detectors of this type was straightforward and that the
detectors exhibited low leakage current at 77 K, although full
X-ray detection characteristics remain to be published. The
signal processing electronics for pixel array detectors are
particularly challenging but Porro et al.21 successfully applied
their DePMOS readout technology, also used for SDD read-
out, to provide time-variant filtering and what was claimed to
be zero added reset noise for pixel array detectors. A compact,
low-power CMOS device was reported by Bastia et al.22 for
providing reset and pileup rejection circuitry for pixel array
detectors. Fanti and co-workers23 described a portable read-
out and acquisition system comprising a USB data interface
and suitable for use with a 256 by 256 Medipix2 pixel readout
chips. Finally, Ercan and co-workers24 reviewed the pixel
array detector systems that have been developed at Cornell
University in the USA.
Not to be outdone by truly pixellated detectors, a strong
team with members in Milan, Munich and Berlin reported25 a
four-element silicon semiconductor detector comprising four
15 mm2 SDDs on a single substrate arranged around a central,
laser-cut hole. The four SDD channels offered excellent energy
resolution of o140 eV at 5.9 keV and the ability to process
very high data rates. An extremely efficient geometry was
obtained with this annular SDD array, which, when combined
with excitation using an X-ray tube and a polycapillary X-ray
optic or SR delivering high intensity excitation through the
central hole, provided a very effective, if rather costly, X-ray
element mapping spectrometry system. The system was used to
good effect in applications such as archaeometry, fine art and
biological studies. A more conventional, but more complex
and costly, approach was described26 in which 13 Si(Li)
detectors, conventionally-cooled by liquid nitrogen, were built
into a single cryostat and set up to detect X-rays from the same
geometric point. A complete pulse processor chain was used
for each detector and, perhaps unsurprisingly, the detector was
installed at a beam line at ESRF, Grenoble, and used for hard
X-ray microanalysis. Once optimised, the system was reported
to offer a 10-fold reduction in acquisition time compared with
the use of a single Si(Li) detector. In the area of less exotic
Si(Li)detectors, Sokolov and colleagues27 described the state
of their art in the development of electrically-cooled Si(Li)
detectors. In their latest system a low power (60 W) Klimenko
cycle cooler was used and an energy resolution of 135 eV at
5.6 keV was obtained for a 20 mm2 device and 1 kcps output
rate, compared with 164 eV for an equivalent setup that used
Peltier cooling. Other than improved stopping power from the
4–5 mm thick Si(Li) devices, it is difficult to see how such an
approach offers significant advantage over modern SDDs that
require lower power yet provide improved energy resolution
and much higher count rates. A novel double layer silicon PIN
detector was described28 in which two, 6 mm2 and 500 mmthick silicon PIN diode detectors were mounted one in front of
the other. Each detector had its own read-out and pulse
processing channel and the reported energy resolution was
220 eV at 5.9 keV when operated at �35 1C. Although offering
significantly better stopping power for the 15–30 keV range, a
single 1 mm thick device would offer less complexity for
straightforward EDXRF applications where increased stop-
ping power is particularly important. The structure of the
assembly also introduced some inevitable contamination
peaks, although those were acceptable for the X-ray astron-
omy application for which the device was designed.
A commercially available avalanche photodiode detector
(APD) was studied by Yatsu et al.,29 who reported that the
detector had the best energy resolution seen to date for an
APD. The measured energy resolution was a rather unexciting
377 eV at 5.9 keV when the 3 mm diameter device was
operated at �20 1C but a very impressive maximum count
rate of 108 cps was obtained and the device was shown to be
extremely radiation-hard. The device also had an encouraging
depletion depth of 130 mm. A study by Ogasawara et al.,30 also
on a commercially available APD, reported an energy resolu-
tion of around 1 keV over the 2–20 keV energy range.
However, the authors’ application was for the detection of
low energy electrons so a depletion depth of only 30 mm was
suitable for their work providing the dead layer was thin,
which it was found to be for this device. Such a device is
unattractive for EDXRF applications and APDs seem likely
to remain of limited interest for X-ray spectrometry generally.
An interesting paper by Cola et al.31 described the novel
electro-optical Pockels effect and how it could be used to
determine the electric field distribution and charge transport
1306 | J. Anal. At. Spectrom., 2007, 22, 1304–1332 This journal is �c The Royal Society of Chemistry 2007
properties in CdTe detector structures. The results provided a
unique insight into the effect of detector bias, diode structures
and contact types, and the method could be used to improve
performance in CdTe detectors, which already offer some
useful attributes in a number of EDXRF applications.
The area of cryogenic X-ray detectors based upon super-
conducting tunnel junctions (STJ) or microcalorimeters/
bolometers continues to migrate during the review period to
the margins of XRF analysis. The attractiveness of ultra-high
energy resolution a decade ago seemed to outweigh the
practical challenges of actually deploying the technologies
and led to a high degree of interest, particularly in the
microanalysis community. That interest is now greatly dimin-
ished and interest in cryogenic detectors is now left to those
engaged in SR X-ray and X-ray astronomy experiments where
the technology challenges are better aligned with their needs,
capabilities and funding. It is, however, perhaps worth draw-
ing attention to the use of STJ array detectors for: metal
speciation;32,33 materials and device fabrication;34–37 charac-
terisation and modelling;38,39 and the design of a novel TES
layout that could lead to very large arrays of detectors for use
in X-ray astronomy.40
Finally, Smith41 joined ancient and modern in a review of
the use of gas proportional detectors in SR X-ray experiments.
3 Spectrum analysis, matrix correction and
calibration procedures
3.1 Spectrum analysis
All EDXRF detection and signal processing systems suffer to a
greater or lesser degree from pulse pileup which increases
continuum background and causes specific sum peaks in the
measured spectrum. Most electronic pulse processing systems
provide a degree of electronic pileup protection but none can
completely eliminate pileup effects, particularly at higher
count rates and the typical dead times of 430% used in many
real-life measurements. Barradas and Reis42 briefly reviewed
the existing numerical methods for correcting pulse pileup and
proposed an extension to a previously published analytical
algorithm that was based on first-principles statistical analysis
and required knowledge of very few system parameters. De-
tails were given of the first and second order pileup corrections
and of the simple iterative scheme used in their approach.
Some impressive results were shown for continuum and sum
peak correction in PIXE spectra from a selenium target but the
n3 channel scaling of the statistical approach meant that
calculation times for a 1 k spectrum were in the range of ‘‘a
few seconds to less than a minute’’, which limits the applica-
tion of this approach and makes it unsuitable in practice for
X-ray mapping and fast, high count rate applications such as
alloy sorting.
The estimation and correction of spectrum background is
critical for accurate XRF analysis and Verkhovodov43
reported an interesting study on three sources of spectrum
background in a WDXRF spectrometer. The author studied
background for: characteristic lines of the material of the
blades of the secondary collimator; secondary radiation from
the sample scattered by the same blades; and scattered radia-
tion from the dispersing crystal of the spectrometer, which was
in the Cauchois geometry. Measurements were made using a
scintillation detector at the spectrometer exit slit with and
without the dispersing crystal being in place. These measure-
ments on a series of 22 samples containing elements in the Z
range 4–83 enabled the identification of the background
components from the collimator blade but showed no signifi-
cant effect from radiation scattered from the dispersing crystal,
in contradiction to a previous study. The corrected back-
ground was to provide a reliable method for estimating sample
mass absorption coefficient based upon the ratio of corrected
background at 0.30 and 0.75 A and the new method was used
to good effect in the analysis of Ag, Pd, Rh and Ru in
metalliferous powders. Monakhov and co-workers44 reported
a so-called ‘envelope method’ for the estimation and removal
of background in WDXRF spectra. The details of this algo-
rithm were given, which was a straightforward search algo-
rithm to find spectrum background points and then connect
them with a straight line, or better a parabolic spline. The
method was shown to be effective for the estimation and
removal of background in model spectra of Conostan oil
reference samples but no experimental data were considered
and special care or pre-processing was required when noise
was small or generated downward spikes in the spectrum. The
specific background shoulder on XRF peaks excited by the
59.5 keV radiation from an 241Am radioisotope source was
shown by Uroic et al.45,46 to be due to Compton scattering of
the source line by the material of the source itself. The authors
showed how careful source system design could help minimize
this effect and their calculations of the source-induced
shoulder were shown to be in good agreement with experi-
mental spectra.
The subject of peak shape in EDXRF spectra was poorly
represented in the review year with only a single paper,47
which considered the theoretical peak shape for Pb K spectra.
Of particular concern to these authors were satellite lines due
to multiple ionizations in Pb and, more particularly, the
generation of those effects by light and heavy projectiles at
various energies. Details were given of the theoretical calcula-
tion based upon multi-configuration Dirac–Fock methodol-
ogy and the authors investigated 12 different satellite lines and
showed the detailed K spectra that contained them. The
complexity of the K spectra simulated by the authors should
act as a salutary reminder to all XRF spectroscopists using
simple models for the estimation of the K series XRF lines of
high Z elements that their bliss in achieving excellent practical
data may be tempered by selective ignorance of the underlying
complexity.
3.2 Matrix correction and calibration procedures
The use of empirical or theoretical coefficients for the correc-
tion of matrix effects remains widespread and Rousseau,48
who has for many years developed and taught the topic,
provided an excellent tutorial on correction methods using
such coefficients. The mathematical models of Lachance–
Traill, Claisse–Quintin and Rousseau were all covered in detail
and all of the variables in these models were described and
presented such that numerical values could be substituted to
This journal is �c The Royal Society of Chemistry 2007 J. Anal. At. Spectrom., 2007, 22, 1304–1332 | 1307
study practical application of these important models. The use
of theoretical influence coefficients for matrix correction in
samples of intermediate thickness was described in very read-
able detail by Sitko.49 The correction algorithm was derived
from the Sherman equation and built upon earlier work where
significant simplifications were made such that fixed coeffi-
cients could be used. Such an approach was applicable only to
limited mass thickness and composition ranges and the new
algorithm was developed to remove these limitations by means
of theoretically calculated variable coefficients. The depen-
dence of the calculated coefficients upon mass thickness and
composition was explained and shown in detail and impressive
results were obtained for a number of samples such as Black
Shale and other geological RMs, few-element spinels and
ferroelectric ceramics in the range from 1 to 5 mg cm�2. The
proposed calculation method was straightforward and the
factors affecting accuracy were also presented for the guidance
of those considering the use of this attractive approach.
An interesting experimental setup was described by Bielews-
ki and co-workers50 for the correction of absorption effects in
the mEDXRF analysis of glass microspheres. Excitation was by
means of a high power molybdenum target X-ray tube oper-
ated at 45 kV and 40 mA coupled with a monocapillary X-ray
optic that provided a 15 mm diameter beam. An SDD, capable
of measuring at high rates (250 ns shaping time) was posi-
tioned behind the samples to measure the direct beam and
calculate the absorption factors and the particle diameters and
an 80 mm2 Si(Li) detector was used to collect the XRF
spectrum that was used to determine analyte peak intensities.
Combination of the two data sets with the proposed correction
algorithm allowed the authors to improve the accuracy of
analysis by up to 28%, for groups of 12 or 16 NIST glass
microspheres of 25 or 40 mm diameter, compared with other
methods of extracting sample particle diameter based upon
optical microscopy or X-ray backscatter. Approximations
were made in this approach for the excitation in that an
‘‘effective wavelength’’ for each analyte line was established
by means of the direct, transmitted spectrum and the author
also identified a rather stringent limitation that the particle
diameter could only be established reliably by this direct,
primary beam method if the particles/grains were all of
identical or very similar chemical composition.
The use of fundamental parameter (FP) calculations for
matrix corrections is widespread but the algorithms can also
be used to calculate from first principles the complete X-ray
spectrum. Just such an approach was reported by Elam and
colleagues51 who were able to model spectra for several
compounds covering a wide range of compositions and also
included scattering of the tube anode characteristic peak,
continuum and the Compton scatter peak. An FP method
was used by Pavlinsky et al.52 for the challenging situation of
C in a high Z matrix but good agreement was reported
between the theoretical and experimental C K intensities from
various carbon-containing compounds. In work also on heavy
element matrices, in which excitation was achieved using the
59.5 keV line from an 241Am radioisotope source, Icelli53
reported good agreement between theoretical and experimen-
tal Compton and Rayleigh peak intensities for BaO, CeO2,
La2O3, Nd2O3 and Sb2O3 samples. The author used the
Rayleigh to Compton ratio in a practical method to determine
the effective atomic number of these high Z oxides, which
could then be used in a number of matrix correction proce-
dures. It is also worth mentioning the report by Shanker54 on
the calculation of Bremsstrahlung produced by the impact of
2–30 keV electrons on thick solid targets, which may be useful
for comparing with other models used for the tube spectrum in
FP correction calculations.
In what was a very sparse year for the application of
chemometrics to XRF spectrometry, the only paper reviewed
was a comprehensive review by Luo.55 The techniques of curve
fitting, multivariate calibration and pattern recognition were
discussed in detail and applications for fields other than X-ray
or gamma spectrometry were also included. The author
focused on the use for XRF spectrometry of genetic algo-
rithms, neural networks, the more-recent support vector ma-
chine and pattern recognition and made clear some of the real
pitfalls as well as attraction of the methods. In concluding, a
hybrid combination of genetic algorithms and neural networks
was proposed as the most likely route to the wider application
of chemometric methods in XRF, although there was no
compelling reason to abandon yet our armoury of fast,
accurate and trusted methods based upon well known FP
and empirical calibration and correction models.
4 X-ray optics and microfluorescence
Capillary and polycapillary optics continue to attract interest in
the development of XRF microanalysis as shown by Sun and
Ding,56 who undertook further work to characterise the
properties of a polycapillary X-ray lens. In particular, they
measured the energy dependence of the focal spot size, trans-
mission efficiency and output focal distance, all of which are
influenced by the dependence on X-ray energy of the critical
angle for total internal reflection. They used a low powered
X-ray tube and a high count rate detection system to overcome
the technical limitations of previous work. Bjeoumikhov
et al.57 discussed the principles and characteristics of X-ray
capillary optics, with particular emphasis on intensity gain,
focal spot size and beam divergence. Their specific interest was
in XRD applications. Lin et al.58 described a new method of
measuring the divergence of X-ray beams from various types
of capillary based on Bragg’s Law. The use of ‘needle type’
collimators was investigated by Tsuji et al.59 and Matsuda and
Tsuji60 in an application designed to excite and analyse small
volumes (estimated to be 0.24 mm3) inside soft tissue samples
(oyster was used as an example). The instrumental configura-
tion used such a collimator to define both the primary and
fluorescence X-ray beams and delineate the detected volume.
Performance data for an agar sample were reported to be 85,
154 and 8 mg kg�1 for the detection limit of Ca, K and Zn,
respectively. A report that significantly extended the concept
of capillary optics was presented by Beuthan et al.61 Their
interest was in the use of capillary fibre optics to realise the
concept of an endoscope for XRF analysis and they prepared
an artificial scattering material containing zinc oxide nano-
particles and clusters to simulate cell layers. Encouraging
results were observed with contrast in the XRF image being
1308 | J. Anal. At. Spectrom., 2007, 22, 1304–1332 This journal is �c The Royal Society of Chemistry 2007
an order of magnitude greater than that of a conventional
optical image.
Other forms of waveguide can also be used to define X-ray
beams and Hertlein and colleagues62 presented a detailed
description of the production of multi-layer X-ray optics using
sputter deposition methods and the characteristics of their
application for making X-ray analytical measurements. Lee
et al.58 made an important contribution in understanding the
role of resonance modes in X-ray waveguides based on thin
films by showing that X-ray reflectivity was extremely sensitive
to the electron density distribution in the thin film. This
realisation resulted from experiments on thin films into which
had been embedded gold nanoparticles, which altered the
waveguide properties.
In the field of X-ray imaging, a scanning X-ray analytical
microscope was developed by Katsuta and colleagues63 speci-
fically to measure sedimentary layers associated with lacus-
trine sediments from Lake Suigetsu, Japan, which were
associated with volcanic eruption events. Interpretation of
results provided millennial-scale variations in the Holocene
that could be correlated with ice-rafting events in the North
Atlantic. Patterson et al.64 used micro-XRF combined with
FTIR imaging to investigate the ageing of polydimethylsil-
oxane foam. Species of particular interest in understanding
this process were residual tin, organotin functional group
moieties and the presence of nitroplasticisers from an exogen-
ous source. This work built on a previous study that had
shown tin to migrate to the foam upper surface and the
authors noted the role of stannous 2-ethylhexanoate as the
polymerisation catalyst. Benedetti et al.65 described the ana-
lysis and evaluation of the phase composition of samples a few
mm in size in cultural heritage studies. Awareness of the
capabilities of confocal XRF microscopy in the elemental
imaging of three-dimensional objects in a variety of applica-
tions was raised by Patterson and Havrilla.66
Of course, synchrotron beams have substantial advantages in
any micro-XRF configuration, being high brilliance focused
beams, although there continue to be technical challenges in
maximising resolution. However, Gelfi et al.67 reported that
although in the field of metallurgy SR experiments have been
undertaken with beams smaller than 1 mm, developments in
high resolution and large area detectors (such as the image
plate detector) have allowed conventional laboratory X-ray
sources to be used to achieve spatial resolutions of a few tens
of mm. The authors described the use of this laboratory-based
micro-fluorescence technology complemented by micro-XRD
to characterise deposits from superheater tubes of solid waste
incinerators with a view to understanding corrosion mechan-
isms. In contrast, Nogita et al.68 used the micro-XRF beam-
line at SPring-8 to characterise the segregation of strontium in
a modified hypo-eutectic aluminium–silicon alloy. Experi-
ments showed that Sr exclusively segregated into the eutectic
silicon phase with important implications for the modification
of this eutectic alloy. A combination of SR techniques (micro-
XRF, micro-XRD and micro-XANES) were used by Martinez
et al.69 to measure the solid-phase speciation of Zn in metalli-
ferous organic-rich surface soils and found that highly cova-
lent Zn–organic bonds were present, explaining in part why
metal partition coefficients are generally higher in organic soils
and why toxic thresholds for total metal concentrations are
higher in organic as opposed to mineral soils.
Finally for this section, Minogue et al.70 described an ultra-
high throughput, micro-XRF technique for the double combi-
natorial screening of peptide–metal binding. The method is tag-
free and sensitive in providing a rapid and quantitative means
of identifying metal–ligand interactions.
5 Synchrotron radiation
Mineral elements, often at the trace level, play a considerable
role in the physiology and pathology of biological systems.
Metallogenomics, metalloproteomics, and metallomics are
among the emerging disciplines that are critically dependent
on spatially resolved concentration maps of trace elements in a
cell or tissue, on information from chemical speciation and on
metal-binding coordination sites. Lobinski et al.71 presented a
review paper on recent progress in element profiling at the
genome scale, biological trace element imaging, identification
and the quantification of chemical species in biological envir-
onments. Imaging techniques covered by this publication
included PIXE, m-SRXRF, SIMS and laser ablation ICP-
MS. Information on oxidation states was obtained from
nano-flow chromatography and capillary electrophoresis
coupled with element specific ICP-MS and molecular-specific
electrospray MS/MS. Synchrotron radiation based techniques
in the form of EXAFS and XANES provided crucial specia-
tion of elements in the micro-samples. The authors recognised
that the increasing sensitivity of EXAFS and XANES now
benefit from the availability of more intense synchrotron
beams and efficient focusing optics and presented information
on oxidation state, fingerprint speciation of metal sites and
metal-site structures.
5.1 Instrumentation
Several instrumental novelties were published during this re-
view period. The SPring-8 facility is well known for its intense
high energy flux, particularly suited for the excitation of
K-shell radiation of elements with high atomic number.
Nishiwaki et al.72 exploited this feature in a forensic non-
destructive examination of small glass fragments (o1 mg) to
analyse 34 elements, in particular Ba and rare-earth elements,
with mono-chromatic excitation energy of 116 keV. The Ce to
Ba ratio was used as an effective parameter for identification,
coupled with information on trace levels of Bi, Cs, Mo, Pd and
Sb, and enabled the authors to develop a useful index for the
discrimination of the glass samples. There has been a long
lasting dispute as to whether the REE L-lines, overlapped by
the K-lines of major elements in a sample, can be de-con-
voluted and quantified in an adequate manner for such
forensic applications. However, in utilising high energy SR-
XRF, this powerful excitation source enabled the authors to
overcome all such critical concerns. Eba and Sakurai73 devel-
oped an image plate detection system for 2D-imaging (8 �8 mm2) in combination with XAFS analysis for combinatorial
substrates of manganese–cobalt spinel and lithium ferrite.
Because no x–y scans of the sample were needed, the method
drastically reduced the total analysis time, with an exposure
time of 1–3 s per pixel reported to be sufficient. Hence,
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combinatorial libraries could be screened very rapidly and
efficiently, using this X-ray imaging system. Woll et al.74
developed a confocal XRF microscope for depth profiling of
historic paintings; in particular, the excitation radiation passed
through a borosilicate monocapillary, whereas a borosilicate
polycapillary was used in front of the detector for the fluor-
escence radiation of interest. In a test painting, four distinct
layers ranging from 10–80 mm were claimed to be differen-
tiated. The next step was reported to be a large area scanner
for 3D imaging that is currently under construction.
There is an emerging trend to combine several synchrotron
radiation-based micro-analytical techniques at certain storage
ring beam lines. The amalgamation of m-SRXRF, m-EXAFS
in fluorescence mode, m-XANES and m-XRD provides com-
prehensive data for the characterisation of samples. Both the
speciation and local distribution of phosphorus in fertilized
soil was investigated by Lombi et al.75 down to nano-levels.
Phosphorus availability is often a limiting factor in crop
production around the world. However, for wheat grown in
calcareous soils, fluid fertilisers were shown to be more
efficient than granular products. Using nano-XRF, the
authors showed that P was invariably associated with Ca
rather than Fe; moreover, nano-XANES indicated that the P
precipitation was in the form of octa-calcium phosphate which
is known to hinder the P exchangeability. This process was less
prominent when fluid fertilisers were applied to the soil. It is
hoped that this kind of research will assist in efforts to help
relieve hunger in developing countries. A plant-based diet is
known to contribute to iron deficiency, resulting in a major
human nutritional problem. Kim et al.76 used XRF m-tomo-
graphy to visualise Fe in Arabidopsis seeds, a model organism
for studying plant sciences, including genetics and plant
development. This work enabled the authors to demonstrate
that iron was localised primarily in the provascular strands of
the embryo in the Arabidopsis seeds. Such localisation was
found to be completely abolished when the vacuolar iron
uptake transporter was disrupted. Bulska et al.77 studied the
distribution and local speciation of selenium in roots and
leaves of onions in vivo by m-XANES and confocal m-XRF,
without the need for any form of pre-treatment or subsequent
sample preparation. The plants were grown in a standard
medium containing inorganic selenium compounds. Using
both analytical techniques, the authors reported that the ratio
of inorganic to amino acid selenium compounds differed in
various sub-parts of the plant. Kashiwabara et al.78,79 deter-
mined the distribution of As and K plus the oxidation state of
arsenic in the roots of a fern, Pteris vittata L. by K edge
XANES. They prepared their specimens by freeze-drying. The
concentration of As was found to increase from the base to the
tip of the roots whereas the K content remained almost
constant. The oxidation state of arsenic at the tip of the roots
was predominantly AsIII, whilst that at the base was AsV.
Chlorine speciation in environmental samples was reported by
Leri et al.80 with reliable XANES measurements in plant, soil
and natural water down to the 5–10 mg g�1 range. They were
able to distinguish between inorganic and organic chlorine as
well as aliphatic and aromatic organic chlorine. Brugger
et al.81 used the combination of m-XRF and m-XANES on
the Eu L3 edge to determine the distribution and valence state
of Eu in scheelite (CaWO4) collected from hydrothermal gold
deposits in Western Australia. The XANES spectroscopy
revealed the coexistence of Eu2+ and Eu3+ in both scheelite
samples. Farges et al.82 studied the speciation and weathering
of copper in ‘‘copper red ruby’’ medieval flashed glasses from
Tours cathedral. Using m-XRF and m-XANES/EXAFS at the
Cu K edge, the authors found two main types of red glasses
with distinct Cu speciation. In the first type, Cu was present in
sub-micron metallic nucleates co-existing with monovalent Cu
(30:70 at%), whereas the second type (feuillete glass) showed
mostly monovalent Cu. The feuillete glasses were also weath-
ered at their surface with a formation of amorphous CuII
species related to a copper sulfate.
Cement-based materials play an important role in multi-
barrier concepts developed worldwide for the safe disposal of
industrial and both low- and intermediate-level radioactive
waste. A group from the Paul Scherrer Institute, Switzer-
land,83–86 studied the Co and Ni uptake in cement by
m-XANES and m-XRF methods with the aim of improving
the understanding of immobilization processes at the molecu-
lar level. XRF mapping revealed a highly heterogeneous
elemental distribution. The X-ray absorption studies showed
that NiII formed layered double hydroxide phases, whereas Co
was found to be present in the oxidation states CoII and CoIII.
Van Oort et al.87 studied the micro-scale distribution patterns
of Pb and Zn in sub-surface soils using synchrotron based
m-XRF. At a depth of 70 cm, the Zn accumulation was found
to be predominantly associated with clay-iron coating whereas
there was no significant correlation between Pb and Zn.
However, at a depth of 100 cm, a clear Pb accumulation was
observed in distinct iron coatings whereas a correlation be-
tween Fe and Zn was absent. Kirpichtchikova et al.88 used
synchrotron based m-XRF in combination with m-EXAFS,
chemical extraction and thermo-dynamic modelling to study
the speciation and solubility of heavy metals in contaminated
soil. The most abundant contaminant was reported to be Zn
(1103 mg kg�1) followed by Pb (535 mg kg�1) and Cu (290 mg
kg�1). The authors studied the extractability of these three
elements and found that the lower extraction level measured
for Zn was due to a zinc phyllosilicate component that was less
soluble than zinc phosphate and zinc ferrihydrite.
5.2 Applications
In this section of the review, consideration is given to those
papers that demonstrate the development of SRXRF in rela-
tion to medical and biological applications. One of the main
threats to human health from heavy metals is associated with
exposure to Pb leading to chronic diseases of the nervous,
hematopoietic, skeletal, renal and endocrine systems. Lead
exposure in industrialised countries stems from the workplace,
leaded pipes and, up to the 1980s, from leaded gasoline;
therefore, most adults have already accumulated a substantial
body burden of Pb. Diseases or conditions with increased bone
turnover, such as osteoporosis, pregnancy, hyperthyroidism
and hyperparathyroidism are associated with increased mobi-
lisation of Pb from the skeleton. Ageing-associated release of
bone-lead into circulation is a potentially important source of
soft-tissue lead exposure and toxicity. Surprisingly little is
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known about how lead is distributed in bone and cartilage
at the microscopic level. Zoeger et al.89 presented a study in
which four macroscopically normal femoral heads and
three patellas were taken from randomly selected forensic
autopsies. All subjects had died from acute illnesses, had no
history of work-related exposure to Pb and had no metabolic
bone diseases. The elemental distribution of Ca, Pb, Sr and Zn
in the chondral and subchondral region was detected using
high resolution SR induced m-XRF analysis in confocal
geometry with a lens also in front of the detector for depth
defined area scans and for 3D-reconstruction. The authors
undertook SR measurements at HASYLAB, beam line L, with
typical area scans of 41 � 41 pixels (400 � 400 mm2), a
measuring time of 5 s per pixel and an inspected volume of
22 � 14 � 20 mm3. A highly specific accumulation of Pb was
found in the tidemark of articular cartilage (the transition zone
between calcified and non-calcified articular cartilage) and
interestingly a correlation between Pb and Zn was reported.
Finally, a complete 3D-reconstruction of the elemental
distribution was presented. Hu et al.90 studied the effect of
Zhugu capsule on osteoporotic rat bone by means of SR and
NAA and found an increased content of Ca, Sr and Zn.
Farquharson et al.91 correlated the distribution of Cu and
other trace elements with the concentration of cancer cells in
human breast tumour specimens by a combination of elemen-
tal mapping and high resolution light transmission imaging.
Perez et al.92 examined lyophilised kidney sections from
normal and arsenic-treated rats to show their 2D elemental
distribution using a collimated white synchrotron spectrum. A
correlation between the distribution of As and Zn was
observed.
Other applications related to art, geology and environmental
studies have also benefited from studies using SR-XRF. The
traditional and acknowledged approach to examining spatially
resolved, rare pieces of art by m-PIXE with an external proton
beam was challenged during this review period by m-SRXRF
(BAMline at BESSY II, Berlin). Reiche et al.93 performed
measurements on a series of silverpoint drawings from the
17th century by Rembrandt Harmensz van Rijn, kept nowa-
days at the Kupferstichkabinett of the State Museums of
Berlin. The data increased the existing database on metal
point drawings, thereby reinforcing art historical assumptions
on the dating of drawings. Cauzid et al.94 studied several single
or two phase fluid inclusions in samples from the Brusson gold
deposit (Italy). The authors claimed to have developed a
standardless quantification procedure and compared it with
previously published, internal and external standardisation
procedures. Their standardless method yielded more accurate
results than the existing standard procedures, but they ad-
mitted that there were uncertainties in results for low atomic
number elements depending upon the inclusion depths. Naga-
seki et al.95 preferred a ‘‘relative intensity’’ approach for the
quantitative analysis of fluid inclusions in synthetic quartz. Ma
et al.96 studied the elemental distribution and morphological
information in individual rain droplets by m-SRXRF to specify
their chemical properties. The authors employed their so-
called collodion replication technique for the indirect determi-
nation of the droplet diameter after the evaporation of the
original water matrix with the elements of interest remaining
as residue. This interesting technique provided a means for the
quantification of masses at the femtogram level.
6 TXRF
A number of review papers on developments in TXRF have
been published in the current period. Streli97 covered the
principles of TXRF as well as a wide range of applications.
Challenges of TXRF for surface and thin layer analysis were
summarised by Klockenkamper.98 Markowicz et al.99
described the activities in the IAEA XRF Laboratory in
Seibersdorf, the philosophy of training in methodology and
applications of XRF techniques in IAEA developing member
states with an emphasis on both quality assurance and control.
An example of a member state contribution on QC was the
publication by Owoade et al.100 dealing with the estimation of
uncertainties in TXRF calibration. A comprehensive overview
of recent developments in TXRF may also be found in the
proceedings101 of the 11th Conference on TXRF and related
techniques.
6.1 Instrumentation
Improvements in detection limits can be achieved either by
integration of X-ray optics (to increase the intensity of the
exciting radation) or by using new higher efficiency detector
types. Korotkikh102 proposed a way of reducing the diver-
gence obtained from X-ray optics using one curved mirror by
adding a second mirror. The benefit of this change was to
increase the intensity of the exciting beam by a factor of 4. An
impressive detection limit of 1 pg for nickel was reported by
Waldschlaeger.103 He used a combination of a microfocus low
power X-ray tube with a larger area silicon drift detector
(SDD) in an optimised geometry. Pahlke et al.104 adapted a
commercial TXRF analyser for wafer surface analysis by
replacing the originally large area SiLi detector with a
10 mm2 silicon drift device. Although the area of the SDD
was smaller by a factor of 8, detection limits were only a factor
of 2 worse, due to the improved detection geometry.
There have been some fascinating developments in micro-
analysis combined with TXRF. Micro-TXRF was first
reported by Tsuji et al.105 The authors performed elemental
mapping from residue samples by reducing the area seen by
the detector down to that of the sample spot. This was
achieved by using pinholes, with diameters ranging from 1
to 0.1 mm, mounted in front of the detector. The same
innovative group also developed a TXRF instrument using a
polycapillary lens106 followed by a horizontal slit to reduce the
divergence in the beam, so that the expected angular behaviour
of the fluorescence signal in TXRF was observed. This in-
strumentation was evaluated by analysing single particles on
silicon substrates. Sparks et al.107 successfully investigated the
applicability of an automated nanolitre deposition system for
semiconductor samples following the work of other groups as
a non-instrumental way of achieving m-TXRF.
A number of other interesting developments have been
published during the current review period. Resonant X-ray
Raman scattering was studied by Szlachetko et al.,108 who
made an important contribution by reporting cross sections,
which were very helpful for background correction when
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silicon wafers were measured with an excitation energy just
below the silicon K edge. Okhrimovskyy and Tsuji109 pub-
lished a numerical approach for depth profiling based on
three-parametric Gaussian profiles. Using grazing exit XRF,
the algorithm enabled the authors to construct depth profiles
of atoms implanted in a substrate. Novikova et al.110 applied
the standing wave technique (grazing incidence XRF) in an
investigation of molecular organisation in Langmuir–Blodgett
films of a liquid crystalline lanthanide complex deposited on
silicon substrates.
6.2 Synchrotron radiation induced TXRF
There has been a considerable increase in the number of SR-
TXRF publications in the current review period describing
particular innovation in complementing elemental mapping by
m-SRXRF with speciation data obtained by XANES, which is
referred to as SR-TXRF-XANES.
Streli et al.111 used this combination of techniques for
arsenic speciation (AsIII and AsV) in xylem sap of cucumber
plants and achieved very good detection limits of As of
170 ng l�1. The authors also reported further results for
aerosols and trace elements in aluminium oxide. These mea-
surements were performed at Beamline L at HASYLAB,
Hamburg, Germany. Osan et al.112 used the PTB laboratory
at BESSY, Berlin, Germany, to apply the SR-TXRF-XANES
technique to low Z elements. They reported the ammonium to
nitrate ratio in Antarctic fine aerosols collected from less than
2 m3 of air. For Antarctic fine aerosols in the size range of
0.25–0.5 mm, nitrogen was observed to be present almost
entirely as the ammonium species. When the size of aerosol
particles increased in the range of 0.25–2 mm, the content of
ammonium decreased and that of nitrate increased. Both
groups drew attention to the considerable advantage of SR-
TXRF for aerosol analysis in that a short collection time was
sufficient to gather enough sample mass for analysis to provide
a means of monitoring rapid changes in aerosol composition.
The increasing interest in linking TXRF measurements with
speciation data (SR-TXRF-XANES) was also supported by
an increase in the use of a chemical pre-treatment approach
instead of XANES. Samek et al.113 used a sequential leaching
technique to investigate the speciation of selected metals (Ca,
Fe, K, Pb and Zn) in aerosol samples. The aim of this work
was to investigate the mobility of these elements in order to
ascertain which components were harmful to works of art.
Fittschen et al.114 published a new technique for the deposi-
tion of standard solutions by inkjet printers and its applicability
for aerosol analysis. Droplet sizes of 50–200 mm were achieved
(which are smaller than the available synchrotron beam) and
the authors reported an absolute calibration of the number of
droplets versusmeasured Co intensity. These results lead to the
conclusion that this technique is very promising for the
quantification of aerosol samples collected by those impactors
that produce a pattern and not a single spot.
SR-TXRF applied to environmental monitoring was
published by groups working at LNLS, Campinas, Brazil.
De Vives et al.115 analysed tree rings from samples of wood
collected from a specific species, Caesalinia peotophoroides,
which is common in Brazil in both urban and country areas.
The samples were digested prior to measurement by
TXRF and the authors found a decrease in the K/Ca, K/P
and Pb/Ca ratios towards the bark. The same group re-
ported116 the use of fish samples as environmental monitors
and discussed the risks to human health by the ingestion of fish
contaminated by metals and other toxic elements. The ability
of Tillandsia (an epiphyte widely used as an atmospheric
monitor) to accumulate heavy metals was successfully tested
by Wannaz et al.117 to provenance atmospheric emission
sources in Argentina.
In the field of clinical applications, Canellas et al.118 deter-
mined trace and major elements in the serum of patients with
chronic myelogenous leukaemia (CML). They found that the
concentrations of Ca, Cr, Cu, Fe, Mn, P, Rb and S differed
significantly between groups of healthy and CML patients.
Serpa et al.119 studied cognitive impairment related to changes
in elemental concentrations in the brain of old rats. Higher Br
and Cu values were found in certain brain regions of the
cognitively impaired group in comparison with the control
group.
6.3 Applications
The determination of Hg was investigated by 2 groups. The
Crete research group led by Kallithrakos-Kontos120 immobi-
lised various complexing reagents on the surface of quartz
reflectors. These authors applied this technique to the analysis
of Hg in sea-water121 and achieved good detection limits of
0.4 mg l�1. A similar approach for Hg determination was
reported by Custo et al.122
Various medical/clinical applications of TXRF have been
reported showing the applicability of TXRF in that field.
Varga123 assessed the possible contamination problem from
steel needles in liver biopsies, but concluded that no measur-
able Fe contamination was detected. Ostachowicz et al.124
analysed cerebrospinal fluid and serum of patients suffering
from amyotrophic lateral sclerosis (ALS) and included low-Z
elements down to Na. Lower values of Mg, Na and Zn and
higher values of Ca were found in the ALS group. Platina in
the plasma of chemotherapy patients was investigated by
Greaves et al.125 after pipetting ml amounts of blood plasma
on to a reflector without using any sample preparation. The
blood of seals from the North Sea was analysed by Griesel
et al.126 who proposed a method suitable for additional
biomonitoring for the health assessment of seals in terms of
electrolyte balance and hydration status. Magalhaes et al.127
investigated trace elements in human cancerous and healthy
tissue from the same individual and compared TXRF with
EDXRF. Increased or constant values of Ca, Cu, Fe, K, P and
S and decreased values of Br and Zn were found in carcinoma
tissue. The influence of certain elements in the dynamics of the
carcinogenic process was investigated by Gierat-Kucharzews-
ka et al.128 The authors judged from their results that low
concentrations of Cu, Fe, Ni, Se, Sr and Zn, together with
higher concentrations of Cd, Co, Cr and Pb, in the carietic
teeth could be one of the caries risk factors. Varga129 analysed
iodine in dietary supplement products and used precipitation
of silver iodide to prevent loss of volatile iodine during solvent
evaporation. The author compared the results with data
1312 | J. Anal. At. Spectrom., 2007, 22, 1304–1332 This journal is �c The Royal Society of Chemistry 2007
obtained by ICP-AES and reported serious spectral line over-
lap between the iodine and phosphorus lines.
In comparison with former review periods, few applications
in surface analysis have been found. Hellin et al.130 reviewed
trends in TXRF for metallic contamination control in semi-
conductor nanotechnology. Tsuji et al.131 investigated the
suitability of TXRF for investigating processes on a chemical
microchip. They made measurements of a drying process in a
reaction channel on a flat region of the surface. A linear
calibration curve for Zn from standard solutions was
obtained, leading to the conclusion that TXRF was feasible
for this application.
Hoefler et al.132 determined low Z elements in environmental
samples, especially biofilms used as biomonitors. The element
of interest was carbon as it is correlated to the growth rate of
the biofilm. These biofilms were directly grown on the reflector
without any sample preparation and the linearity of the
carbon calibration curve and its dependence on sample mass
was investigated. This work was undertaken using a specially
designed TXRF spectrometer with a Cr anode X-ray tube as
excitation source, a vacuum chamber and a detector with an
ultra-thin window, all optimised for the detection of low Z
elements. Mages et al133 also analysed biofilms as a biomo-
nitor in mine surface drainage water to determine the influence
of copper mining on the environment. The trace element
content of individual micro-crustaceans (copepod specimens)
and a Brazilian waterweed (Egeria densa) from a metal-con-
taminated Chilean wetland were measured by Woelfl et al.134
The same author135 also used macro-zoobenthos from the
Tisza and Szamos rivers to test whether the zoobenthic fauna
showed an enhanced metal content three years after an
industrial accident in the Romanian mining industry. Fe was
much lower and Mn and Zn much higher in concentration in
benthos from the more contaminated river. The authors
concluded that the benthos was suitable as a bio-indicator
for metal contamination, but the sediment bioaccumulation
factor turned out to be low, offering low bioavailability of the
contamination element for benthic organisms. Gruber et al.136
analysed Austrian wine without any sample preparation and
was able to use elemental fingerprinting to identify the wine
brand, vineyard and the year of vintage of the 11 different
wines tested.
Applications from various other fields were published: Nishi-
waki et al.137 analysed small glass fragments and was able to
distinguish glass fragments by their elemental ratios. This
discrimination could not be achieved by measuring the refrac-
tive index. Metal ion diffusion through polymeric matrices was
investigated by Boeykens et al.138 This work has potential
importance in drug control release, microbiological corrosion
protection and enhanced oil recovery. Uranium was deter-
mined in sea-water by Misra et al.139 whilst Nigerian fossil
fuels were measured by Mokobia et al.140
7 Portable and mobile XRF
Some of the more exciting developments in portable XRF
instrumentation continue to be in the area of planetary
exploration. Much recent interest has centred on the explora-
tion of Mars and, in particular, the discovery of evidence of
water on Mars. The contribution of Mallett et al.141 is, there-
fore, timely in modifying and extending an existing Monte
Carlo code with a view to developing a method for detecting
OH and H2O in Martian rocks and soil. This development was
based on comparing the predicted and measured ratio of
elastically and inelastically scattered plutonium La X-rays
from rock or soil samples measured by the Mars Exploration
Rover’s alpha particle X-ray spectrometer. As this ratio is
sensitive to the mean atomic number of the sample, so the
difference between the predicted ratio, based on an anhydrous
sample, and the measured ratio gives information about the
‘invisible’ (as far as XRF is concerned) elements in the sample.
One of the problems encountered in the design of the Beagle 2
instrumentation package was the conflict between incorporat-
ing both a Mossbauer and XRF spectrometer, both instru-
ments with radioactive sources, in relatively close proximity,
with the potential loss in scientific performance due to
enhanced background radiation levels. Butcher et al.142 con-
sidered these and other issues surrounding the management of
radiation hazards and background effects posed by radioactive
sources for planetary missions. Okada et al.143 continued the
design study and specification for the Japanese SELENE-B
mission to the Moon, which will comprise a static lander and
rover that will incorporate a sample analysis package with an
XRF/XRD. The highest priority for this mission will be to
provide evidence for the origin and evolution of the Moon by
the analysis of sub-crustal material that is exposed at a crater’s
central peak.
Lead (Pb) in soil is one of the more common terrestrial
applications of portable XRF and Clark et al.144 undertook an
important study of the sources, sinks and exposure pathways
of Pb in urban soil in 103 gardens in Roxbury and Dorchester,
Massachusetts, USA, and remarkably found that 88% con-
tained Pb at concentrations above the US-EPA reportable
limit of 400 mg kg�1. Supplementary laboratory (including
isotopic) analyses indicated that the major sources of Pb were
automobile gasolene and Pb-based paint with the latter source
contributing 40–80% of the mass balance. Results from test
crops grown in soil from this locality indicated that consump-
tion of these crops would be equivalent to 10–25% of a child’s
daily exposure from tap water—food for thought! Minimising
the risk of contamination from Pb in soil was the basis of a
study by Dixon et al.,145 who were concerned about the
effectiveness of low-cost soil treatments designed to reduce
exposure to contaminated soil in the ‘yards’ adjacent to
buildings in Boston, MA, USA. The yards recruited for this
study had been treated with ground coverings and ground
barriers in 2000–2001 and were found by PXRF to have fallen
from an average of 2021 mg kg�1 Pb to 206 mg kg�1 a year
after treatment. As a result, the amount of Pb contamination
at the building entry was found to have been reduced by about
20%. Kilbride et al.146 analysed a cocktail of elements of
environmental interest in soil using two types of field portable
XRF and found the results to be broadly comparable with
those from ICP-AES after an aqua regia extraction.
The capability of PXRF for in situ measurements is a major
advantage of the technique, but also gives rise to the problem
that sample surfaces are unlikely to be flat and positioned
exactly in the analytical plane of the instrument, requiring a
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supplementary correction for these surface irregularity effects.
A number of approaches have already been found in the
literature to correct the consequent discrepancies and mini-
mise bias, a topic to which Bonizzoni et al.147 returned in the
analysis of metal objects of irregular shape. Their approach
was to calculate corrective irregular shape factors based on
modifications to the conventional fundamental parameter
approach, which assumes the excitation and detection geome-
try angles are equal and of constant value for all samples.
Applications of PXRF, including the development of innova-
tive instrumental configurations continue to expand in popu-
larity and reflect increasing recognition of the versatility of the
technique. Thus, Emery and Morgenstein148 used a portable
XRF to analyse mud brick used at an ancient town site of El
Hibeh (Egypt) with the aim of establishing the source of this
material from surface sediments in the local Nile floodplain.
Gianoncelli et al.’s interest149 was in the glazes on two
sculptures located in the cathedral of Seville (Spain) in relation
to Florentine production methods during the Renaissance
period. Michelangelo’s statue of David was the object of
investigation for Castellano et al.,150 whose interest lay in
mapping the presence of sulfur to help restorers choose the
most suitable method of treatment for cleaning the statue.
Papadopoulou et al.151 described a portable micro-XRF in-
strument fitted with a monocapillary lens designed for the
analysis of cultural objects and gave some examples of the
quantitative analysis of ancient Greek ceramic samples. The
instrumentation described by Desnica and Schreiner152 for use
in analysing art objects at the Academy of Fine Arts, Vienna,
incorporated a miniature X-ray tube and silicon drift detector
and two laser locating devices. Suzuki and McDermot153 used
in situ XRF in combination with FTIR for the analysis of
titanates, with the specific aim of identifying and evaluating
the frequency of occurrence of the use of nickel titanate
(a yellow pigment) and chrome titanate (a yellow–orange
pigment) in US automobile finishes between 1974 and 1989.
Both these pigments were used as replacements for lead
chromate pigments that were finally withdrawn in the early
1990s. Andrikopoulos et al.154 described a mobile instrument
that incorporated two complementary techniques of consider-
able potential interest, Raman spectroscopy and XRF. The
influence stemmed from the ability to acquire details of the
structural properties of pigments by Raman and their elemen-
tal composition by XRF (including the composition of invi-
sible under-layers). Use of this instrument was validated on an
experimental icon painted using traditional Byzantine techni-
ques and it was found that almost all pigments could be
identified, including those hidden by over-painting. An addi-
tional contribution worthy of mention is the mobile laboratory
XRF application that Shalev et al.155 used to analyse artefacts
and sediments during the field study of a small archaeological
copper smelting site in the Negev, about 30 km west of a
complex of ancient copper mines, in Jordan. Results were
interpreted to estimate the scale of copper production during
the first period of operation at the end of the Early Bronze
Age. Stosnach156 tested a portable TXRF spectrometer for its
suitability for on-site analysis of heavy metal contaminated
areas and compared the results with TXRF measurements
after complete microwave assisted acid digestion. Finally,
Herman et al.157 undertook an interesting study of the health
hazards associated with the use of lead (Pb) in the workplace,
where workers face risk of exposure through inhalation,
ingestion and sometimes through dermal exposure. Risks also
extend to outside the workplace from the inhalation of lead-
contaminated air, the ingestion of lead-contaminated dust and
soil, lead polluted water, lead adulterated food and lead
supplemented medicine. The study involved an evaluation of
lead in blood levels (using an analyser based on the principle of
ASV) and field portable XRF to measure environmental lead
in paint, soil and dust. The results of this study was to reveal a
high incidence of lead toxicity in workers in the lead industry
at four facilities in India and high levels of lead in associated
environmental samples. These results indicate that developing
countries, such as India, have not benefited from the stringent
national and international policies that are now enforced in
many developed countries.
8 On-line XRF
We believe that on line XRF continues to have a key role to
play in a number of industrial processes, but that innovations
remain under-represented in the literature. It is a pleasure,
therefore, to report the work of de Mussy et al.,158 who
described an on- line micro-XRF instrument for assessing
the thickness of copper on patterned wafers during an electro-
plating and chemical mechanical polishing process.
9 Applications
9.1 Sampling, sample preparation and pre-concentration
techniques
Ameasurement process comprises both sampling and chemical
analysis, with sampling being of crucial importance as the
reported result may only be derived from the test portion
presented to the spectrometer. In many applications it is the
sampling phase that generates the highest component of
uncertainty. When sampling brownfield sites, where the in-
herent heterogeneity of contaminants within the site is a major
factor, the literature offers a variety of sampling designs and a
choice of depth and mass recovery with in situ measurement
strategies increasingly being used as a powerful technique to
reduce the overall time taken to complete a survey. Taylor and
Ramsey159 offered a new approach for those concerned with
strategies for sampling contaminated land. Various methods
are currently used to estimate uncertainty, balancing factors
such as cost and fitness-for-purpose, to ensure that subsequent
decisions based on the chemical analyses are acceptable. Their
approach offered the ‘‘optimised contaminated land investiga-
tion’’ method that considered site-specific variables, such as
measurement costs, against the level of uncertainty and sub-
sequent costs that may arise from missclassification of the land
in question. This new method provided an objective and
traceable judgement as to whether the reported chemical
analyses were fit-for-purpose. A similar exercise was reported
by Gustavsson et al.160 who were concerned with a site that
had contaminated ‘‘hot spots’’ where the components contri-
buting to the total sampling error were reduced and the
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analytical error increased. They concluded that the low con-
centration of contaminant, small extracted sample size and
large particles in the collected samples contributed to the level
of uncertainty. These studies are a timely reminder that
analysts should define their adopted sampling strategy to
ensure that the commissioner of a survey of contaminated
land is able to judge whether the reported results are asso-
ciated with an acceptable level of uncertainty to support a
subsequent decision as to the classification of land under
investigation.
This review has followed the development of a technique for
the analysis of small volumes of liquid, typically microlitres to
millilitres, onto thin film substrates and allowing the liquid to
dry into a concentrated residue or ‘‘dried spot’’. The main
advantage over conventional direct liquid analysis is that
liquid matrix effects, such as scattering, are minimised and
the sample analytes are concentrated, thereby enhancing both
the quality and sensitivity of analysis. Miller et al. built on
their earlier work of using nanolitre dried spots that decreased
reagent consumption and produced specimens of uniform
shape to enable the detection of elements with picogram
sensitivity by micro X-ray fluorescence and TXRF. Their
current publication161 overcame the major drawback in the
preparation of nanolitre dried spots due to operator variables
as the droplets were deposited manually through a contact
injection method onto different analysis substrates. This tech-
nique, however, introduced sample preparation errors due to
variations in the contact geometry of the injector tip with the
substrate surface between droplet injections plus a human
factor arising from differences in user technique. Practitioners
will also recognise that the consequence of such a contact
deposition method could be contamination as the tip interacts
with different substrates. The authors explored the use of non-
contact automated printing technology as an alternative
method for the preparation of nanolitre dried spots by dis-
pensing 20 and 50 nl volumes of multi-element standard
solutions onto AP1 and Kapton film substrates. Multiple dried
spots were found to be reproducibly deposited in the same
precise location on the film substrate surface, allowing in-
creased sample loadings for higher element sensitivity. How-
ever, the characteristics of the substrate did affect the quality
of dried spot formation as irregularly shaped spots developed
on the thicker, more hydrophobic Kapton film when higher
droplet mass loadings were attempted. This problem was
overcome by increasing in the area analysed to ensure that
the entire dried spot residue was measured. This method for
sample preparation may also be of interest to readers using
other analytical techniques involving small quantities of
liquid, such as IR, Raman or UV/fluorescence spectroscopy.
An alternative to evaporation for the immobilisation of
trace analytes in aqueous samples has resulted in a plethora
of published work on preconcentration techniques as workers
continue to refine methods and take advantage of new materi-
als. Many methods are application-specific but readers famil-
iar with the damage caused to delicate specimens by the
intense X-radiation from modern 4 kW wavelength dispersive
spectrometers may benefit from the work of Abe et al.,162 who
protected both faces of their specimens with a commercially
available laminate film. Trace amounts of Cd, Co, Cu, Fe, Hg,
Mn, Ni, Pb and Zn in environmental water were pre-concen-
trated with an iminodiacetate extraction disc (IED) which
comprised beads of polystyrene–divinylbenzene copolymer
containing iminodiacetate knitted among its polytetrafluor-
oethylene (PTFE) fibres. The high extraction rate and volume
offered by these discs was preferred when compared with
column and static ion-exchange methods. Subsequent lamina-
tion of the IED was reported to prolong measurement times
from 7 to about 200 min when irradiated at 4 kW whilst
negligibly decreasing the detected signal from the analytes of
interest. It was, of course, necessary to reduce the power of the
X-ray tube to 1.5 kW to compensate for Hg evaporation. The
authors reported linear calibration curves over the range
500 mg to 5 mg with detection limits corresponding to three
times the standard deviation of the blank intensity of 0.1–
0.4 mg for Co, Mn and Ni, 0.5–0.8 mg for Cu, Fe, Pb and Zn
and 7 mg for Cd. A spike test for 10 mg of eight analytes,
excluding Mn, showed good recoveries (90–100%) for muni-
cipal tap water and rainwater. Fontas et al.163 compared two
different types of membrane used for the concentration and
determination of CrVI in electroplating water from galvanic
baths. The anion-exchanger extractant, Aliquat 336, was
selected for the enrichment of Cr using (a) an impregnated
membrane, where the organic solution of the extractant filled
the pores of a polymeric membrane, and (b) a polymer
inclusion membrane, prepared by physical inclusion of Ali-
quat 336 in the matrix formed by either cellulose triacetate or
poly(vinyl chloride) and the plasticizer 2-nitrophenyl octyl
ether. Both types of membrane were reported to be stable
and efficient, with the polymeric membranes made of PVC
showing a higher degree of homogeneity in terms of metal
distribution. The EDXRF data from the preferred PVC-based
membranes gave a linear calibration curve over the concentra-
tion range 0.3–8.8 mg L�1 with a detection limit of 0.3 mg L�1.
Orescanin et al.164 offered a procedure for the determination
of lanthanides in environmental samples after separation from
the major matrix elements on Dowex 50W-X80 resin followed
by pre-concentration with the chelating agent ammonium
pyrrolidine dithiocarbamate (APDC). The influence of pH of
the solution and presence of organic matter on the complexa-
tion was investigated using certified reference materials and
environmental samples of red mud. Whilst maximum recovery
was reported at pH = 8, the presence of organic matter
slightly modified the complexation giving higher recovery at
pH = 7. However, it was interesting to note that recovery
varied from 91.4% for Pr to only 24.9% for Dy. The EDXRF
spectrometer used a 109Cd source for excitation of the La lines
of the lanthanides.
Other preparation techniques included an investigation by
Manara et al.165 of the behaviour of sulfur in silicate glasses
and melts used for the incorporation of radioactive waste.
Sulfates are known to have low solubility in the vitreous phase
and the authors investigated the relationship between the
ratio, R, of Na2O to B2O3, from variations in the type of
sulfate added and the effect of V2O5 on the incorporation of
sulfates in borosilicate glasses. The oxides were melted in Pt/
Au crucibles in air. The work confirmed that the incorporation
process is favoured by the network depolymerisation that
evolves with the ratio R. It was found that V2O5 accelerated
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the kinetics of sulfur incorporation in the glass by modifying
the borate network and fostering the formation of voids
compatible with the sulfur co-ordinate polyhedron in the
glassy network. The study also found that the kinetics of
X2SO4 incorporation was slower when X = Cs. Celik and
Oner166 compared the characterisation of narrowly sized
fractions of clinker ground by a ball mill and high-pressure
grinding rollers. A higher degree of liberation of mineral
phases resulting from inter-granular breakage along grain
boundaries was attributed to the high-pressure grinding roll-
ers, thereby improving the properties of the final cement
product.
9.2 Geological and industrial minerals
Because of its capability of measuring a range of important
major and trace elements, XRF continues to be widely used in
supporting geochemical research, in part because of the way
analytical results can contribute to an understanding of geo-
chemical processes. In many of these studies, XRF is one of a
number of techniques that is used to contribute data. Thus,
Cutten et al.167 used XRF to ‘fingerprint’ the composition of
sandstone and schist conglomerate clasts from the Maruia
Basin, adjacent to the New Zealand Alpine Fault, to identify
source terrains and hence understand fault movement over the
last 11.5 Ma. Ostrooumov and Banerjee168 used XRF as one
of the techniques to characterise amazonite, a potassium
feldspar, in the Keivy granitic pegmatite from the Kola
Penninsula, Russia. Their particular interest was in the differ-
ent colours (blue through green) found in various generations
of this mineral, with the possibility that the chemical and
spectrometric parameters of this mineral might be an impor-
tant exploration indicator for REE mineralisation. Adams
et al.169 used XRF and EPMA to analyse glass shards from
the San Miguel de Allende graben, Guanajuanto, Mexico,
which, with other stratographic data, was designed to provide
an understanding of the timing of the volcanism, date and age
of extension, and a better understanding of the tectonic and
volcanic evolution of Central Mexico. XRF, XRD and optical
microscopy were used by Sanchez-Munoz et al.170 to study 86
microclines from 7 granitic pegmatites with the aim of under-
standing better the evolution of these species in relation to the
rate of cooling and interaction with aqueous fluids. Moller
et al.’s171 interests lay in climatic changes in the Holocene
period in southwest Greenland as indicated by sedimentolo-
gical and geochemical (XRF) data derived from a 3.5 m
gravity core from Ameralik Fjord. Bahr et al.172 also studied
gravity cores with XRF playing a supporting role to high
resolution stable oxygen isotope data on ostracod shells to
evaluate the late glacial to Holocene palaeoenvironment of the
Black Sea. Their interpretation was that a climate mode like
the North Atlantic Oscillation was governing the inter-annual
variability in the flow of water from the River Danube. Events
contributing to boundary layers are of considerable interest to
geologists and Zhang et al.173 used XRF as one of the
techniques to analyse claystones and mudstones at the Chahe
section (Guizhou, South China) of the terrestrial Permian–
Triassic boundary. The claystones in this section were of
volcanic origin and the absence of spherules provided no
evidence of an extraterrestial impact event. Schroder et al.174
adopted a multi-technique approach to analyse two drill cores
from Agouron, Transvaal, South Africa, to elucidate the
deposition sequence and regional geology. Another interesting
geochemical investigation was a detailed micro-XRF/XRD/
EXAFS study of the mineralogy of natural ferromanganese
coatings on quartz by Manceau et al.175 The coatings com-
prised alternating Fe-rich (ferrihydrite) and Mn-rich (verna-
dite) layers that were irregularly distributed and not always
continuous. The trace elements Ba, Ni and Zn were associated
with vernadite and As with ferrihydrite and the authors gave
full details of the inter-layer structures of these coatings as well
as the substitution mechanisms for the trace elements.
In addition to the mainly ‘hard rock’ studies summarised
above, XRF has contributed to a number of studies on soils
and sediments. The Indian monsoon was a topic of interest to
Von Rad and colleagues176 and in particular its link to climate
change over the Late Holocene period, based on a high
resolution record of laminated sediments deposited off the
coast of Pakistan. The three proxys for climate change were
varve thickness, stable oxygen isotopic ratios and inorganic
geochemical compositional data, all used to infer the monsoon
driven ‘moisture history’ of the northeastern Arabian Sea. The
Cenomanian–Turonian Boundary Event (Cretaceous) was
investigated by Turgeon and Brumsack177 using sediments
from the Umbria–Marche Basin of central Italy in a project
designed to elucidate one of the most spectacular ‘oceanic
anoxic events’. McCarty et al.178 undertook a meticulous
investigation of the relationship between composition and
lattice parameters of some sedimentary dolomites of various
composition, location and age. The main outcome was to
determine the relationships between the lattice parameters and
the Ca-content in non-stoichiometric dolomite. A study of the
geochemistry of soils on a catena on basalt at Khon Buri,
northeast Thailand, was carried out by Thanachit et al.179 who
described the geochemical characteristics of soils developed on
the crest, backslope, footslope and valley floor on an undulat-
ing basaltic lava corrosion plain. It was found that element
behaviour in these soils could be categorised as the Al, Ca, Fe
and Mn groups.
Geologists often avoid weathered surfaces, preferring
freshly broken surfaces to overcome the difficulty weathering
causes in rock recognition and geochemistry. However, weath-
ering is rather an important process, not the least in the
evolution of soils. Taboada et al.180 used XRF to measure
the Th and U concentration and SEM to study the corre-
sponding mineralogy of the rock and soils developed on
granitic rocks in northwest Spain, with determinations made
on rock, bulk soil, and then in the sand (50–200 mm), silt (2–
50 mm) and clay (o2 mm) fractions. Although the bulk soil had
similar concentrations to the rock, the U and Th concentration
in the sand fraction was always lowest and that in the clay
fraction highest (always higher than that of the rock). Leach-
ing of U and Th from the top to the bottom soil horizons
appeared to be the major influence on the environmental
impact of these elements, noting the risk of redistribution in
the potentially airborne fraction. The same authors181 under-
took an analogous study of the behaviour of Ti and Zr and
found that Zr was enriched in the silt fraction (at a
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concentration of up to 5 times that of the parent rock), whilst
Ti was enriched in both the silt (up to 5 times) and clay (up to
12 times rock) fractions. Weathering was also of interest to
Jones et al.,182 but more in the manner of how to compensate
for it. The aim was to use portable XRF to assess geochemical
variations within and between rock outcrops of spotted doler-
ite on the Preseli mountains in SouthWales, a project linked to
the origin of some of the blue stones at Stonehenge. The
sampling strategy involved making two neighbouring but
independent measurements on the weathered rock surface at
a number of locations across the outcrop with the intention of
measuring the within-outcrop and between-outcrop variabil-
ity. Several outcrops were heterogeneous at the 5% signifi-
cance level for one or more elements and geochemical
differences were demonstrated between some of the outcrops
using discriminant analysis.
Rocks are not often directly associated with a radiation
hazard, although all contain naturally occurring isotopes of K,
Th and U, often at enhanced concentrations in granites. Brai
et al.183 correlated radioactivity measurements and air kerma
rates (i.e., a measure of the radiation dose in air) with
geological features of Sicily. Samples of rocks and soils which
contributed to this study were analysed by XRF. Geochem-
ical, mineralogical and petrographic features were in good
agreement with radiometric data, allowing an evaluation to be
made of the public health implications of natural radioactivity.
Because of the concentrations of K, Th and U, granite used as
a building stone or for ornamental purposes also carries a
small risk of exposure to ionising radiations, as highlighted by
Salas et al.,184 who collected 100 samples of granite from
traders in Balo Hoizonte, Brazil. These samples were analysed
by a range of techniques, including XRF, which showed that
some samples contained up to 30 mg kg�1 U and 130 mg kg�1
Th. The radiation hazard was calculated by assuming a
standard room tiled with granite containing more than
60 mg kg�1 U and Th. The estimated radiation dose was
between 0.11 and 0.34 mSv year�1, which is significantly lower
than the international exposure limit of 1.0 mSv year�1.
Another radiation-related geochemical contribution concern-
ing the geochemical environment surrounding a shallow geo-
logical repository for radioactive waste was presented by
Akagawa et al.185 This work addressed the issue of redox
fronts formed in fractured crystalline rock caused by the
infiltration of oxidised pore water and was based on measure-
ments of a redox front in Cretaceous granitic rocks in central
Japan. XRF, ICP-MS and EPMA showed that REE, Cs and
U had migrated to the front with U enriched at the front edge,
probably retained by Fe-oxyhydroxides. The authors sug-
gested that matrix diffusion in the oxidising zone could be
an effective way of retarding the release of contaminants.
A few technical advances in XRF methodology have been
published in the current review period. Although glass disks
are almost universally used for the XRF determination of the
major elements, chromite ores present a number of challenges
because of their highly refractory nature. However, Sanchez
Ramos et al.186 undertook an in-depth study to optimise the
preparation of chromite ore glass disks and recommended the
following experimental conditions: lithium tetraborate as flux
at a sample to flux ratio of 1 to 40 with the addition of one or
two drops of lithium bromide solution; fuse for 30 min at
1200 1C. The authors prepared calibrator disks using similar
reference material and different high purity ignited oxides to
obtain calibration curves for Al, Ca, Cr, Fe, K, Mg, Mn, Na,
Si and Ti (as oxides) and gave satisfactory accuracy. Nakaya-
ma et al.187 described a comprehensive scheme for the XRF
analysis of felsic rocks for 42 oxides and elements based on 1:1,
1:2, and 1:10 sample:flux glass disks. ‘Low dilution’ glass disks
of satisfactory homogeneity with a 1:1 flux to sample ratio
were prepared using a double fusion method in which the melt
was allowed to cool to room temperature before the second
heating stage. The scheme involved the determination on 1:10
glass disks of the major elements and Rb, Sr, Y and Zr: on 1:2
glass disks—As, Ba, Co, Cr, Cu, Ga, Nb, Ni, Pb, Th, U, V, W,
Zn and on 1:1 glass disks—Cs, Hf, Sc, Sn, Ta and REE. Safi et
al.188 investigated the chemical analysis of phosphate rock
using different methods, but highlighting modern XRF in-
strumentation. Evaluations are not often published concern-
ing the effectiveness of the calibration function in XRF
analysis, however Guevara et al.189 undertook a comparison
of linear regression models for quantitative geochemical ana-
lysis, using XRF as an exemplar, including ordinary least
squares fitting, weighted least squares and maximum like-
lihood fitting, and concluded that the latter two approaches
were statistically more consistent.
XRF has been applied to a number of aspects of the
processing of industrial minerals, including a study by Banza
et al.190 that was designed to reduce the processing time to
reduce the Fe content of glass grade sand for special glass
applications. XRF was used to monitor the Fe content (pre-
sent in the raw sand as pyrite) and in place of a ‘dump leach’
process that took several weeks, an acid leach (with an
investigation into the effect of the continuous addition of
H2O2) resulted in a five-fold reduction in the Fe content over
a period of 2 d. Olubambi et al.191 also used XRF as part of a
study to optimise the recovery of base metals from a complex
sulfide ore from Ishiagu (Eboyin State, Nigeria). The extrac-
tion of ferronickel, as part of the mining process, left a residual
solid (scum) of a vitreous material that created an environ-
mental problem. Hernandez et al.192 investigated this material
using XRF, XRD and EPR. This ‘scum’ was found to
comprise oxides rich in Fe2O3 and NiO as well as enstatite
and a-alumina and Fe3+ glassy phases and the study repre-
sented the first exploratory stage to identify a potential
application that would reduce this environmental problem.
Bernaus et al.193 undertook a multi-technique study of Hg in
the mining district of Almaden in Spain, using SR-based
techniques and micro-EXAFS. Part of the study was to assess
the potential availability and part to understand its mineral-
ogy and elemental associations. Cinnabar was one of the main
species in the Hg-rich particles studied, together with more
soluble mercury compounds such as schuetteite and mercur-
y(II) oxide.
9.3 Environmental
9.3.1 Atmospheric particulate matter. As industrial socie-
ties have become more aware of the extent of particulate
matter that we inhale, legislation has been put in place to
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reduce such pollution, resulting in the need to measure and
monitor concentrations in ambient air. This, in turn, has
resulted in an improvement in air quality and a reduction in
the concentration of heavy metals analysed. It is expected that
the regulatory limits will continue to be reduced, thereby
challenging analysts to develop methods with sufficient sensi-
tivity to meet any new need. In recent years, this review has
commented on the increasing ability of EDXRF systems to
satisfy analytical needs that had previously been the domain of
wavelength dispersive configurations. Literature under review
during this current period and discussions at XRF confer-
ences5,6,194 have demonstrated the ability of polarised EDXRF
spectrometers to achieve the expected lower limits of detec-
tion. Therefore, as the expected concentration of atmospheric
particulates collected by samplers falls, attention turns to the
homogeneity of the filters presented for analysis. Owoade
et al.195 utilised the enhanced sensitivity of polarised EDXRF
in their study of the uniformity of particulates collected by a
PM10 sampler when the size of the incident X-ray beam was
less than the diameter of the filter. Each filter sample was
divided into four quadrants with each quadrant analysed using
the same conditions. All sixteen analytes were detected in
every sample with less than 10% deviation in concentrations
between quadrants for most analytes except Ba and Cs, where
the deviation was of the order of 20%. The authors concluded
that the PM10 sampler was reliable in terms of homogeneity of
the deposition and where analytes were found at low concen-
trations, it was important to ensure that sampling time be
increased to enable a higher mass deposition on the filter.
Attitudes towards the disposal of waste have changed as
people recognise the need for waste separation and recycling of
products and materials to create a sustainable society. In
Sweden, the deposition of combustible waste to landfill was
prohibited in 2002 and the city of Boras responded by
introducing new incinerators at their district heating plant.
Ahoh et al.196 used EDXRF to characterise the elemental
contents in PM2.5 aerosols collected in the city dominated by
this modern waste incineration plant. Ambient air is a complex
mixture of gasses and particles, and this study recorded data
on particle mass and black carbon together with SO2 and NO2.
Using principal component analysis (PCA), five major sources
of the collected PM2.5 were identified: the waste incineration
plant itself together with other local sources; oil incineration,
biomass burning, long-distance transport and traffic emis-
sions. The authors were aware that the quantitative contribu-
tion from these different sources must be considered only as
informative, since the number of observations was small
compared to the number of identified variables and further
work is expected. Moving indoors, Wang et al.197 determined
the chemical composition of the PM2.5 fraction from incense-
burning in a large environmental chamber. Chemical analyses
by XRF for elemental species, ion chromatography for water
soluble organics (ammonium, chloride, nitrate, potassium,
sodium and sulfate) and thermal/optical reflectance analysis
for carbon were performed for the combustion of three incense
categories (traditional, aromatic and church incense). The
average organic carbon and elemental carbon concentrations
in the PM2.5 were church incense 4 traditional incense 4aromatic incense. The inorganic ion concentration sequence
was traditional incense 4 church incense 4 aromatic incense
and the elemental profiles were found to be dominated by Cl,
K and Na. Readers with an interest in the analysis of fine
aerosols down to 0.25 mmwill find comment on the application
of SR-TXRF in section 6.2 of this review where the advantage
of this technique is described for the analysis of low mass
samples.
Harper and Pacolay198 continued their extensive series of
studies of workplace air quality that compared various types of
sampler used for the collection of lead in different environ-
ments for subsequent presentation to a portable XRF analy-
ser. In this investigation personal samples were taken at a
manufacturer of solder alloys consisting mainly of lead and
tin. The same five samplers were assessed, namely: the close-
faced 37 mm cassette (CFC), the 37 mm GSP or ‘‘cone’’
sampler, the 25 turn Institute of Occupational Medicine
(IOM) ‘‘inhalable’’ sampler, the 25 mm button sampler and
the open-face 25 mm cassette. Mixed cellulose ester filters were
used in all the samplers. Following XRF analysis, the sample
filters were digested in acid and analysed by ICP. The internal
surfaces of the CFC samplers and 25 mm open-face cassettes
were also wiped, and the wipes analysed for lead to assess wall-
losses in these two samplers. In addition to Pb, other metals
(Ag, Cd, Cu, Fe and Sb) were detected in some or all of the
samples by ICP analysis, but only Cu and Fe could be
determined by the PXRF under test. All five samplers gave
good correlations (r2 4 0.9) between the two methods over the
entire range of found Pb mass, which encompassed both the
action level and the permissible exposure limit enforced in the
USA. The average of three readings across filters from the
GSP sampler gave the best result: however, analysis of the
wipes from the interior of the cassettes showed a substantial
loss of sample to the walls. Even larger wall losses were
recorded in the 25 mm open-faced cassette. Neither this
sampler nor the IOM or button samplers met the 95%
criterion.
9.3.2 Other environmental studies. XRF analysis is now
widely accepted as the technique of choice for the analysis of
not only atmospheric particulates collected on filters but also
precipitates of river and lake sediments, suspensions, rocks
and minerals, etc. An empirical method for correction of matrix
effects in samples collected on membrane filters was proposed
by Sitko.199 Better sensitivities and detection limits, especially
for low Z elements, are generally obtained for thin samples in
comparison with thicker ones due to the small or negligible
absorption effects and associated low background. However,
many samples collected on filters are, in fact, of intermediate
thickness and manifest absorption and enhancement effects.
Therefore, an improvement in the quality of data from these
intermediate samples can be achieved if experimental or
mathematical correction methods are employed. Sitko’s ap-
proach for the analysis of elements from Z = 19 (K) to Z =
92 (U) used the familiar ratio of coherent (Rayleigh) to
incoherent (Compton) X-ray intensities but also recognised
the fact that, in the case of samples collected on filters, the
coherent and incoherent scattering observed was the sum of
the contributions from both the filter and the material
collected. Measurements were made using a WDXRF
1318 | J. Anal. At. Spectrom., 2007, 22, 1304–1332 This journal is �c The Royal Society of Chemistry 2007
spectrometer, fitted with a Mo target X-ray tube, of Ka lines
for elements from K to Sr: La1 lines for Ba, Ce, Cs, La, Nd, Th
and U and Lb1 for Pb. Net intensities were collected for each
sample by measuring the analyte peak and the continuum
close to the peak. Samples of geological reference materials
(silicates and aluminosilicates) and fly ash were collected on
two types of membrane filter: Sartorius (acetate, 0.2 mm pore
size and 47 mm diameter) andMillipore (type RA, 1.2 mm pore
size and 47 mm diameter). The Sartorius filter was found to
scatter X-rays to a greater extent and thought to be due to the
difference in mass per unit area between the two filters (4.81
and 4.46 mg cm�2 for Sartorius and Millipore, respectively).
The validity of the algorithm was reported to be satisfactory
for samples of mass per unit area between 1 and 3 mg cm�2
and indicated its usefulness for the filters and samples tested.
The search for safer materials to prevent the release of heavy
metals into the environment continues. All ships have their
underwater hulls treated with antifouling (AF) paint in order
to minimise operating expenses. The treatment increases the
speed of a vessel through the water, reduces noise and
decreases fuel costs but has a negative influence on the
environment. Whilst the use of tributyltin is subject to world-
wide restriction and will be completely prohibited in 2008,
alternative AF paints continue to use copper and organic
biocides. Valkovic et al.200 used EDXRF to determine the
concentration of the biocidal elements As, Cu, Pb and Zn plus
Br, Ca, Cr, Fe, K, Mn, Ni, Rb, Sr, Ti and Y in surface
sediments from Kvarner Bay on the Adriatic coast, where the
high density of boats and restricted tidal movements was a
concern. The same laboratory201 also studied surface and core
coastal sediments in Punat Bay and Soline Bay, Croatia, to
demonstrate the negative environmental influence of marinas,
shipyards and ports caused by restricted water exchange in
these bays with the open sea. In common with many other
environmental investigations, the authors used their data to
produce contour maps and perform factor analysis to
strengthen the influence of their work. Concentrations in mg
kg�1 were 1.1–524.4 for As, 5–12 640 for Cu, 3–1430 for Pb
and 12–11 860 for Zn and the authors hoped to use these
results to contribute to a proposal for remediation measures
on the Adriatic coast. Lebow et al.202 reported a statistical
analysis of their data on the influence of soil and wood
properties on the leaching of As and Cu from yellow pine
sapwood treated with chromated copper arsenate. Specimens
were leached by an accelerated laboratory method for 12
weeks in different soils or in water. XRF was used to measure
the loss of As and Cu and correlated with various physical and
chemical soil properties. The average loss of copper was
reported to be approximately equal to or greater than the
arsenic loss for specimens exposed to soil whereas, for those
leached in water, the arsenic loss was twice that of copper loss.
This study suggested that ground-contact leaching should be
employed for realistic depletion measurements of copper-rich
preservatives and that the data would be helpful in the
development of a standard laboratory method for the timber
industry.
The systematic classification of plants began in 1735 and was
formally postulated by Carl von Linne with additional genetic
aspects introduced by Charles Darwin in 1859. The Linnaean
system has followed basically the same fundamentals until
today, and has caused great discord amongst taxonomists
since it is still based on visual inspection. As analysts, benefit-
ing from the wealth of data produced by XRF and other
instrumental techniques plus the awareness of accuracy, we
can appreciate the confusion due to such a subjective classifi-
cation. Chemical methods based on the determination of
proteins in a species were proposed and used to clarify some
impasses and to assist in the classification of family species or
of a specific variety. These chemical methods were destructive
and also time and reagent consuming, therefore new methods
were urgently needed to end the controversy caused by the
classification system. Alexandre and Bueno203 have developed
a reliable, non-destructive method for the classification of
seeds of species and varieties of carnations and species of
banana using conventional EDXRF combined with chemo-
metrics and both PCA and hierarchical cluster analysis
(HCA). Their method was based on multivariate analysis of
spectra, including Raman scattering profiles that occurred
around the Compton and Rayleigh peaks from organic sam-
ples. It will be interesting to see if taxonomists accept X-ray
scattering spectrometry. Margui et al.204 used selective excita-
tion, from different secondary target materials, in a polarised
EDXRF configuration to solve the familiar mutual interfer-
ence of As and Pb when analysing trace levels in different
vegetation species collected at two mining areas in Spain.
Cadmium was also measured using the Ka line. A standardless
fundamental approach (IAEA QXAS) was adopted to deter-
mine other metals in the absence of suitable certified reference
materials and to compensate accurately for self-attenuation
effects in the samples. Arsenic speciation was described by
Mihucz et al.,205 who combined off-line layer chromatography
with TXRF and applied the technique to As speciation in root
extracts of cucumber plants. Xu et al.206 studied the cellular
distribution of Mn in the toxic, accumulator plant Phytolacca
acinosa. The intention was to obtain essential information on
metal toxicity and the bioaccumulation mechanism. As a
result, Mn was identified as a key player in the detoxification
mechanism of Phytolacca acinosa. This plant, also known for
its high biomass and fast growth, was found as a good
candidate for phytoremediation of manganese-polluted soil.
The analysis of other environmental samples in the future
will benefit from the workers at NIST207 who have recently
extended their collection of environmental SRMs that began
in the late 1960s with the introduction of fuel and biologically-
related materials. Those who have joined programmes to
generate CRMs will be familiar with the difficulties experi-
enced when recruiting contributing analysts. Advances in
analytical methodology, including multi-element isotope dilu-
tion mass spectrometry (IDMS) and expanded instrumental
neutron activation analysis (INAA), have enabled value-as-
signment based on fewer but better characterised independent
analytical techniques. The advantages of IDMS for the deter-
mination of Hg and S and multi-element small sample air
particulate matter (SRM 2783) serve as examples of the new
approach by NIST. Developments in the production of SRMs
included the issue of fresh-frozen biological materials and of
jet-milled natural matrix materials with improved homogene-
ity, such as a highly homogeneous air particulate matter and
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sediment SRMs for small sample analytical techniques. Terai
et al.208 reported the synthesis of CrVI in portlandite,
Ca(OH)2, suspensions for the immobilisation of hazardous
hexavalent Cr. Solutions of 0.1 mol L�1 of NaAlO2 and CrO3
were prepared in deionised water which were then mixed with
portlandite suspensions and stirred for 3 h in a CO2 free
synthetic air. Ca:Al atomic ratios were varied from 1.0 to
5.0 against Cr:Al atomic ratios of 1.0, 1.5 and 2.0. By using a
combination of XRF, XRD and ESEM the authors found that
CrVI–ettringite formed at pH 10.9 and associates with calcite.
No CrVI–ettringite was found below pH 10.9. A comprehen-
sive review of all analytical techniques for environmental
analysis may also be found in our companion Atomic Spectro-
scopy Update.209
9.4 Archaeological, cultural heritage and forensic
Some of the more interesting contributions in these categories
this year involve the analysis of inks, papers and parchment,
and indeed can truly be regarded as extending from the ancient
to the modern. The ancient often features, so commencing
with the opposite end of the time scale, Trzcinska210 was
interested in developing a method for classifying black powder
toners used in laser printers and copiers for obvious forensic
reasons. Discrimination was based on the use of Fourier
transform infrared spectrometry to distinguish the polymer
used in the toner and EDXRF to distinguish the inorganic
elemental content. Some 95.8% of pairs of samples could be
distinguished on the basis of FTIR and EDXRF spectra, with
the long term aim of creating an appropriate database. This
work appears to be a development of a related publication by
the same author.211 FTIR, Raman spectroscopy and XRF
were the combination of techniques used by Zieba-Palus and
Kunicki212 to characterise blue and black ballpoint pen and
gel ink and found that 90% of the samples could be distin-
guished using these methods. Gall inks used in works of art
were the topic of analysis by Hahn et al.,213 who included
measurements of pencils and coloured crayons by micro-XRF
in their studies to fingerprint compositions that characterise
gall inks used by an individual artist and to establish a
chronology of use. EDXRF was the technique of choice of
Manso and Carvalho214 to identify different types of paper
used in the production of an Italian book published in 1941.
The elements Ba, Ca, Cu, Sr, Ti, Zn could be used in a
principal component analysis approach to show that the book
was manufactured using three different types of paper—an
interesting development that could have forensic applications.
Although many applications of XRF are published each
year, few if any cover the authentication of postal pieces.
However, Sanchez and Valentinuzzi215 used XRF as one of
a number of complementary techniques to analyse different
inks used on stamps, postmarks and postage stamps. Spatial
resolution was achieved by use of micro-collimators and
mono-capillaries and the results could be used to authenticate
postal pieces through the elemental composition of the inks.
A number of studies directly related to forensic applications
have been published in the current review period. One of the
more interesting was the work of Worley et al.216 in the
detection of visible and latent fingerprints by micro-XRF,
based on the inorganic elements present in the print. The
major advantage of this approach was that the prints are left
unaltered by this process. Key elements for imaging were Cl
and K, although Al, Ca, Mg, P, S and Si could also be
detected, and it was reported that the success of this approach
could be person- or diet-dependent as the prints from one
subject could not be detected by this process. The character-
isation of small glass fragments217,218 is a relatively common
forensic application, and the role XRF might play in con-
tributing Sr data to the multi-technique characterisation of
elephant ivory to control the illegal trade219 is also expected,
but the investigation of gun shot residues is a little more
unusual. This study, by Berendes et al.220 was designed to
develop a method to visualise gun shot residue patterns caused
by the use of heavy metal-free ammunition to determine
shooting distances as well as the general composition of
particles. A millimetre-resolution XRF spectrometer was
found to offer a significant reduction in analysis time com-
pared with m-XRF and distribution patterns of Ga, K and Ti
provided the appropriate visualisation. A further study with
direct human interest was undertaken by Rebocho et al.221 to
measure the lead uptake of human bones from the Middle
Ages using portable XRF instrumentation. Significant con-
tamination by Pb of spongy bones that had been kept in a lead
coffin was reported (250–350 mg Pb g�1 bone mineral) com-
pared with 4–7 mg Pb g�1 bone mineral, for bone buried in soil.
The analysis of paints and pigments is one of the more
visually attractive applications of XRF with examples this
year that span the investigation of materials and techniques,
through to conservation. In the area of conservation, Cotte
et al.222 investigated the blackening of the Pompeian paintings,
which have a deep red colouring associated with the use of
cinnabar (HgS) as a pigment. SR-based micro-XRF revealed
‘peculiar’ distributions of Cl and S, which were confirmed as
degradation products by X-ray absorption spectrometry as
Hg–Cl compounds and gypsum, formed by calcite sulfanation.
Angelini et al.223 used the chemical characterisation of the red
decorative pigment and of the stone surface of the Capestrano
Warrior (Archaeological Museum of Chieti, Italy) by portable
XRF as an example of a non-destructive testing method that is
very important to conservators and art historians. Aceto
et al.224 used portable XRF and Raman to investigate the
degradation of an alloy pigment on an ancient Italian manu-
script (Homilies on the Gospels of Gregory the Great), datable
to the IX century. Probably because of conditions of storage,
part of the decoration (described as being ‘of golden fashion’),
which was found to be an alloy of Cu, Pb and Zn, had
degraded to inorganic Cu salts, which gave it a green colora-
tion. The non-invasive properties of EDXRF (together with
reflectance spectroscopy) were used by Bonizzoni et al.225 to
reconstruct layers on Renaissance paintings executed on wood
or canvas. Civici226 used TXRF to characterise the palette in
five Albanian icons painted by Onufri Qiprioti (16th to 17th
century). The palette included white lead, calcium white, gold,
orpiment, yellow and red ochre, vermilion, red lead, a copper-
based green pigment and smalt. This study was extended by
Pavlidou et al.227 to include data by m-FTIR, optical micro-
scopy and SEM, which showed the presence of calcium
carbonate as the main component in all pigments, pointing
1320 | J. Anal. At. Spectrom., 2007, 22, 1304–1332 This journal is �c The Royal Society of Chemistry 2007
towards a fresco technique. In the study of ancient Egyptian
boat models, TXRF was claimed by Huhnerfuss et al.228 to
have the potential to dissipate some uncertainties when apply-
ing classical archaeological dating methods based on the
analysis of pigments.
Because of its capability for fingerprinting samples for
provenancing studies, XRF remains a popular choice of
technique in the analysis of pottery and ceramics. One
approach is to employ multivariate statistical analysis to
categorise samples, as exemplified by the work of Papachris-
todoulou et al.229 in demonstrating different local production
practices from EDXRF data on 64 potsherds from Orraon,
northwestern Greece. Bakraji230 and Bakraji et al.231 used a
radioisotope XRF instrument to separate archaeological pot-
tery samples from Katana and from the Tel Kouzama site near
Damascus, Syria, into four distinct groups. The second com-
mon approach is to use EDXRF as one of a suite of techniques
selected to characterise artefacts. XRD and optical and scan-
ning electron microscopy were used by Giannotta et al.232 to
demonstrate cultural exchanges between Apulia and the Mid-
dle East during the Middle Ages from the results of an
investigation of siliceous paste fragments from an archaeolo-
gical site at Siponto (Foggia, Italy). A similar array of
techniques was used to support XRF in the analysis of Mayan
ceramic figurines from Calakmull (Campeche, Mexico) by
Garcia-Heras et al.233 Results were interpreted as showing
that the manufacture of ceramic figurines could be associated
with workshops linked to a monopoly on ceramic production
performed by centralised influence of the town of Calakmul.
Peng et al.234 used a microprobe EDXRF instrument to
analyse glaze layers on ancient celadon material (1127–1279
AD) from Zhejiang, China and associated their provenance to
Chinese imperial and Chinese popular kilns, whereas Civici235
used XRF to determine the type of raw material used for the
manufacture and provenance of terracotta figurines (3rd cen-
tury BC) found in the Seferan Lake, Central Albania. The
author demonstrated that the figurines were made of local
clays, although it was not certain whether the black external
coating, made of an iron-rich material, originated from weath-
ering under water or had been applied during manufacture.
Moroni and Conti236 were interested in the technology of
pottery production and used a basket of techniques, including
XRF, to analyse the products of firing experiments on two
clays selected to best represent XVIth century ceramic tiles and
wares and proposed that a low rate of heating and the amount
of calcite present in the clay were important parameters when
matching the test pieces with archaeological artefacts. Barilaro
et al.237 were interested in trading patterns of amphorae in the
5th to the 3rd century BC after excavation of amphorae
fragments from southern Italy and used both XRF and FTIR
analysis. Adan-Bayewitz et al.238 found unusually high and
variable adundances of Ag in pottery samples from 38 Ro-
man-period sites in Jerusalem and attributed the presence of
Ag to human origin.
The analysis of glazes can also yield useful evidence of the
provenance of ceramics, as exemplified by the work of Roldan
et al.,239 who used EDXRF to show that elements such as As,
Co, Cu, Fe, Mn, Ni and Zn were characteristic of ‘cobalt’ blue
pigments in glazes on Valencian ceramics manufactured from
the 14th to the 20th century. Colour variations in Hispanic
lustre decoration on late 13th century Hispano-Moresque
potsherd were examined using EXAFS by Smith et al.240 with
a particular interest in the influence of the Cu/Ag ratio. Gold
lustre on Italian Renaissance pottery was of interest to Bon-
tempi et al.241 who extended earlier studies that involved XRF,
which had demonstrated that the lustre comprises a hetero-
geneous metal–glass composite film, formed by Ag and Cu
nanoparticles dispersed in the outer layer of a tin-opacified
lead glaze. Their present study used grazing incidence XRD to
characterise the structure and depth distribution of the Ag
nanoparticles.
Conservation of archaeological artefacts is sometimes a
challenging area of endeavour in which there is considerable
benefit in understanding the mechanism of deterioration.
Carmona et al.242 studied the biodegradation of five stained
glass windows at the Cartuja de Miraflores Monastery (Bour-
gos, Brazil) using UV-Vis spectrophotometry, XRF, optical
and electron microscopy and X-ray microanalysis. Heteroge-
neous dark brown interconnected crusts were found covering
most of the external surface of the glass, together with craters
and pits filled with whitish deposits. Microbial colonisation of
the glass was also observed and both bacteria and fungi were
characterised. Protective glazing can be used to reduce the rate
of deterioration of historic stained glass windows from atmo-
spheric pollutants and particulates and Godoi et al.243 mon-
itored for one year the Sainte Chapelle (Paris), using passive
diffusion tubes, to monitor SO2, NO2 and O3 with EDXRF to
measure the accumulation and re-suspension of particulate
materials. Results indicated the beneficial outcome from the
use of protective glazing. The same pollutant species were
monitored by Worobiec et al.,244 who studied the indoor/
outdoor air exchange and its influence on air quality and the
preservation of works of art in St. Michael Archangel’s
Church, Szalowa, Poland. Suspended particulate material in
this wooden church was generally considered to have an
outdoor source. Laser cleaning has begun to be widely used
in art restoration but requires careful optimisation to ensure
that only contaminants and encrustations are removed and the
original material is not damaged. Hence the need for the study
by Benedetti et al.245 who used m-XRF and m-XRD to evaluate
laser cleaning of a 4th century BC chamber gravesite in
Torricelle, near Nori (Naples). Their preliminary results sug-
gested a possible influence of the laser on the calcite–aragonite
transformation. In a contrasting approach to conservation,
Maravelaki-Kalaitzaki et al.246 treated deteriorated porous
bioclastic limestones from the archaeological area of Aptera,
Crete, with various silicon-based strengthening products and
used EDXRF and FTIR to measure the depth of penetration,
which was up to 30 mm. Improved reinforcement results were
obtained by applying an elastified silicic acid ethyl ester.
Angelini et al.247 were interested in an integrated approach
to the characterisation and conservation of artefacts from the
Brazilian colonial period using XRF and other techniques,
and described the long-term protection of copper-based alloys
by coating them with SiO2-like films using a home-made
reactor fed with a tetraethoxysilane–oxygen–argon mixture.
As with other inorganic archaeological artefacts, XRF
continues to be widely used for the characterisation of metallic
This journal is �c The Royal Society of Chemistry 2007 J. Anal. At. Spectrom., 2007, 22, 1304–1332 | 1321
objects. Cartechini et al.248 used a range of techniques to
characterise the compositional and textural properties of
Etruscan bronzes, in part to correctly assign several fragments
to recompose the original pieces. Although providing indica-
tive data, XRF and SEM/EPMA were strongly affected by
surface alteration and contamination, with neutron diffraction
favoured in providing sensitive information on composition
and phase quantification in a non-destructive manner. Pisto-
fidis et al.249 reported that 3 silver coins from the IIIrd century
found in the ancient Greek cities of Dyrrachion and Korkyra
had different chemical compositions and microstructures, with
XRF being used to provide the compositional results. Inter-
pretation of the multi-technique results gave an insight into
differences in the minting processes. A multi-technique
approach (incuding XRF) was also used by Schwab et al.250
to provenance iron artefacts found at Manching, southern
Bavaria, to a specific source of iron ore near the Danube.
Provenancing of lithic artefacts is one of the simpler applica-
tions of XRF, exemplified this year by the work of Triscari
et al.251 who were interested in the source of volcanic rocks
used in medieval buildings in north-eastern Sicily and southern
Calabria and showed an origin to the Etnean and Aeolian
volcanic areas. In contrast, Negash et al.252 used EDXRF to
provenance 10 Early Stone Age obsidian artefacts from the
Milka Konture site, Ethiopia, to a source located a short
distance away.
9.5 Industrial
Since the implementation of the new EU Directives on Re-
striction on Hazardous Substances (RoHS) and Waste Elec-
trical and Electronic Equipment (WEEE) in July 2006, the
development of analytical methods, including new reference
materials, to control the level of these hazardous substances is
making significant progress. Matsuda et al.253 set up a method
for the determination of Cd, Cr and Pb in shaped brass
samples using EDXRF with polarisation optics. For each
element a calibration curve was set up using bulk CRMs
comprising flat brass standard samples and measurements
were performed with dedicated secondary targets. To take
into account small and shaped samples, corrections were made
using Rayleigh scatter peak intensities. Lower limits of detec-
tion were achieved of 3.3 mg g�1 for Cd, 6.6 mg g�1 for Cr and
29 mg g�1 for Pb, with 300 s measurement time, which were all
significantly lower than the legal limit value of 0.01% m/m for
Cd and 0.1% m/m for Pb and CrVI. Comparison with mea-
surements by ICP-AES proved the validity of this method for
the analysis of small and shaped brass samples. Commercial
requirements have led to the production of new polymer
reference materials. The Japanese Society of Analytical Chem-
istry developed two new types of plastic disc RMs for use in
XRF screening, both described by Nakano et al.254,255 The
former, Japanese language, paper described the certification of
a polyester reference material for the elements Cd, Cr and Pb,
whilst the latter (in English) presented the certification for the
element Hg, also in polyester. Both types of CRMs were
prepared by casting the polyester mixed with a toluene solu-
tion of the relevant organometallic compound. For each
element, five concentration levels were prepared, ranging from
0 to 50 mg kg�1 for Cd, 0 to 200 mg kg�1 for Cr and Pb, and 0
to 250 mg kg�1 for Hg. The certified value, together with the
measurement uncertainty at a confidence level of 95%, was
determined on the basis of the results of an inter-laboratory
study with 21 participants for the determination of Cd, Cr and
Pb, whilst 15 laboratories participated in the Hg certification
process. Song et al.,256 on the other hand, presented a paper in
Chinese concerning the use of in-house reference materials
containing the elements Br, Cd, Cr, Hg and Pb at concentra-
tion levels ranging from 100 to 1500 mg kg�1. Linear XRF
calibration curves were set up and the matrix effect was
corrected by empirical coefficients, using scattered radiation
as an internal standard. The accuracy of the method was
proved by analysis of the certified BCR 681 polymer and a
precision of less than 5.0% was achieved. For the calibration
of XRF spectrometers, Swagten et al.257 described the devel-
opment and the characterisation of homogeneous polyethy-
lene reference materials, using a preparation procedure that
can also be implemented in future projects for other type of
elements. In this contribution the reference materials were
prepared by incorporating additives to ‘‘virgin’’ polyethylene.
The calibration of the reference material was performed using
ICP-AES for the elements Al, Ca, Mg, Na, P, Ti and Zn,
whereas k(0)-NAA was used for the same elements together
with F. Over the complete concentration range, starting from
5 mg kg�1 for Ti up to 600 mg kg�1 for Mg, a good agreement
of the results between both techniques was obtained.
In the framework for reducing the waste burden to the
environment, more and more emphasis is being put on the
recycling and re-use of waste produced in several branches of
industry. Limbachiya et al.258 reported the use of recycled
concrete aggregate (RCA) in concrete production using XRF
for the determination of the elemental composition. XRF
analyses of commercially produced coarse RCA and natural
aggregates showed a comparable chemical composition be-
tween recycled and natural aggregates, and the original source
of RCA had a negligible effect on the major elements. Test
results indicated that up to 30% coarse RCA, as a substitute
for natural gravel, had no effect on the main three oxides
(Al2O3, CaO and SiO2) in concrete, but thereafter slight
changes in composition were observed. Rossini and Ber-
nardes259 reported a laboratory scale study, based on sulfate
roasting for the selective recovery of valuable metals from
galvanic sludge. Of particular interest in this treatment was the
use of two hazardous wastes as raw materials, both generated
in large quantities at coal extraction sites (coal waste/pyritic
waste) and at plating shops (galvanic sludge). The XRF
characterisation showed a high Cu content in the sludge of
more than 14% on a dry base. In the roasting process, the
conditions that best reflected a compromise between the
recovery of the valuable metals and the economic viability of
the process were achieved using a 1:0.4 galvanic sludge/pyrite
ratio, with 90 min of roasting time at 550 1C, which resulted in
a recovery of 50% Cu, 43% Ni and 60% Zn. Additionally, Xu
et al.260 used dried sewage sludge as raw material for the
production of ceramsite, used for the treatment of municipal
waste water. Under the most appropriate conditions, a mix-
ture of dried sewage sludge, water glass and clay was sintered
at 1000 1C, and subsequently characterised by XRF combined
1322 | J. Anal. At. Spectrom., 2007, 22, 1304–1332 This journal is �c The Royal Society of Chemistry 2007
with other analytical techniques. The ceramsite produced was
appropriate for the removal of several contaminants from
municipal waste water.
As can be deduced from the large number of papers
published in this review period, the X-ray fluorescence tech-
nique in combination with other analytical techniques has
proved to be a matured and routinely applied analytical
technique for the characterisation of newly developed cera-
mics, cement samples and catalysts, including the monitoring
of catalytic processes. Readers interested in the performance
of these new materials should also consult the companion
ASU review on Industrial Analysis: Metals, Chemicals and
Advanced Materials.4 Some typical examples are presented in
this review section. Ramos and co-workers261 used both
FAAS and XRF for the quantitative analysis of Pb, S and
Zn in zinc oxide samples, commonly used to make industrial
ceramic enamels. Owing to the high loss on ignition values, the
working conditions for XRF analysis were optimised by
analysing the samples as pellets. For PbO, an accuracy of
1.06% and a precision of �0.06% were obtained, for SO3
4.76% and �0.25%, respectively, and for ZnO 0.46% and
�0.2%, respectively. These values were satisfactory, given that
Pb and S were only present in small amounts. Barba et al.262
adapted a WDXRF methodology previously established by
the authors for the characterisation of chromium-containing
ceramic pigments, in order to analyse cobalt-containing pig-
ments. The chemical and mineralogical evaluation of slag
products derived from the pyrolysis/melting treatment of
municipal solid waste was performed by Saffarzadeh et al.263
This study revealed that the major constituents were glass
(over 95%), oxide and silicate minerals, as well as individual
metallic inclusions. Elevated concentrations of Ba, Cr, Cu, Pb
and Zn were measured in the bulk composition, of which Ba,
Cu and Pb in the glassy phase behaved as incompatible
elements, whereas Cr and Zn were strongly incorporated into
the silicate structure.
Another interesting application was presented by Cernohors-
ky et al.,264 describing the use of a combined fundamental
parameter method for the EDXRF analysis of precious metal
alloys. This method combined the standardless FP method
with an empirical calibration using reference materials con-
sisting of Pt–Ir, Pt–Rh, Pt–Ir–Rh and Pt–Rh–Pd. Results
obtained by this approach agreed well with the corresponding
certified values or ICP-AES results, respectively. Miskolczi
et al.265 determined the sulfur content of diesel fuels and diesel-
fuel-like fractions of waste polymer cracking material, using
both ICP-AES and EDXRF. In the case of XRF analysis, the
effect of various types of thin foils on the accuracy was
evaluated, showing considerable differences and deterioration
of the accuracy as a function of type of foil. An appropriate
correlation was obtained between the results for ICP-AES and
EDXRF analyses, although some differences could be ob-
served, which could be explained by different proportions of
C/H in the samples. Finally, Y. Mino266 presented alarming
WDXRF results of dissolved Sn still present in canned foods,
as had been previously highlighted by other workers. As
sample pre-treatment, a pellet was made from freeze-dried
sample syrup or a homogenate solution of fruit or meat after
dilution with the same weight of cellulose powder. The ana-
lyses of several kinds of canned foods from the Japanese
market, indicated that exceptional concentrations of up to
100 300 mg kg�1 of Sn were present, and a relationship was
observed between the concentration level and the time after
production. Moreover, once a can was opened the amount of
dissolved Sn increased rapidly if the product remained in the
can.
9.6 Clinical and biological
X-ray fluorescence spectrometry takes a prominent place as an
analytical technique for a wide variety of clinical and biologi-
cal applications, as emphasised in several reviews. Garcia
et al.267 described the recent trend in metal-binding and
metalloprotein analysis using a broad range of analytical
techniques, including capillary electrophoresis-SRXRF. The
latest challenges in metallomics were also discussed. Paunesku
et al.,268 on the other hand, reported on the evolution of the X-
ray fluorescence microscopy technique to establish elemental
analysis in cell and tissue samples. Recent examples showed
the maturity of this technique in bio-medical applications,
especially thanks to the development of third-generation
synchrotrons. Chettle269 presented a review dealing with in
vivo trace element analysis of living humans in order to gain
insights into the relationship between chronic exposure to
toxic elements and health effects. The most fully developed
analytical techniques were for Cd and Pb, with the 109Cd shell
X-ray fluorescence being the most widely used.
As an alternative excitation to 109Cd excited K-XRF for the
in vivo measurement of Pb in bone, Cernohlawek et al.270
evaluated the use of X-ray tubes with various anode materials,
filters, as well as different secondary targets and low-Z polari-
sers. Using a portable XRF spectrometer equipped with a
50 W Pd X-ray tube, a Mo secondary target and a Peltier-
cooled Si-drift detector, a promising lower limit of detection of
0.6 mg g�1 for Pb in bone was obtained, determined on a
plaster of Paris phantom doped with a known Pb concentra-
tion and without overlying tissues. Nevertheless, whilst the
research continues for alternative sources, the 109Cd K-XRF
technique remains a well established method, as reflected by
the high number of contributions presenting extended experi-
mental studies on the influence of cumulative Pb exposure on
different health issues. Potula et al.271–273 performed several
studies among female former smelter workers, indicating each
time the negative effect of extended Pb exposure on their
health. The results showed that blood Pb might adversely
affect bone mineral density, that Pb exposure resulted in
higher blood Pb levels, especially during menopause, and that
changes in blood and bone Pb levels over time were associated
with increased bone resorption. Other work on this topic may
be found in Section 5 of this review, dedicated to work using
synchrotron radiation. Both Weisskopf et al.274 and Shih
et al.275 proved that long-term Pb exposure might have
persistent effects on cognitive functions among elderly men.
Martin et al.276 demonstrated that a cumulative Pb dose had
an acute effect on blood pressure and a chronic effect on the
risk of hypertension, whereas other workers277 found evidence
that the intake of low dietary Ca might be helpful in the
prevention of hypertension induced by an elevated Pb burden.
This journal is �c The Royal Society of Chemistry 2007 J. Anal. At. Spectrom., 2007, 22, 1304–1332 | 1323
Besides a broad range of routine measurements, research into
the improvement of detection limits for in vivo measurements
is still in progress as well as for Pb measurements in bone using109Cd278 and Sr measurements in bone using 125I279 as the
excitation source. One particular challenge presented was to
increase the sensitivity for Hg determinations in kidney using109Cd K-XRF for which preliminary results were presented by
Grinyer et al.280
Elemental composition analysis of biological tissues was
studied by Serpa et al.,281 who compared the elemental con-
centration in different brain structures, namely the temporal
cortex, entorhinal cortex, visual cortex and hippocampus,
from female rats of different ages. SR-TXRF measurements
of Al, Br, Ca, Cl, Cu Fe, K, Ni, P, Rb, S and Zn in these
tissues were performed at the Synchrotron Light Brazilian
Laboratory, indicating distributions depending on structure
and ageing. Of particular interest, the authors reported a
correlation between the increase in Fe with ageing in the
hippocampus, since it is involved in oxidative stress which is
recognized as one of the main causes for neuronal death in
Parkinson’s disease. Kwiatek et al.282 evaluated the elemental
distributions of Cu, Fe, Mn and Zn using SRXRF to distin-
guish prostate cancer from hyperplasia. These measurements,
performed on the L-beam line at the HASYLAB, Desy,
Germany, showed elevated concentrations for these elements
in cancerous tissues, as compared with normal and hyperplas-
tic ones.
The use of X-ray fluorescence spectrometry in dentistry
remains a recurring issue. Hurrell-Gillingham et al.283 evalu-
ated the in vitro biocompatibility of a novel Fe2O3-based glass
ionomer cement. Conventional ionomer glasses used in den-
tistry, but also in nose and throat surgery, contain Al3+, a
component linked to poor bone mineralisation and neurotoxi-
city. The substitution of Al2O3 with Fe2O3 was investigated
using both XRF and XRD. The results indicated that the
prepared Fe2O3-based glasses had Al2O3 contamination from
the crucibles and also had undergone substantial F� losses.
Nevertheless, cements could be prepared from these Fe2O3-
based ionomer glasses, and the cement setting times appeared
to be related to the P2O5 content. Moreover, these Fe2O3-
based cements showed good in vitro biocompatibility. A more
lugubrious but interesting study was presented by Bush
et al.,284 who demonstrated the use of portable XRF in
detection and analysis of restorative materials present in
non-cremated, cremated and processed-cremated individuals.
For this extended study 70 unique combinations of resins were
made in six human cadavers and simulated ante-mortem dental
records were created. Firstly, it was demonstrated that the
portable XRF system could be used to localise these restora-
tions in non-cremated individuals and to identify more than
75% of the resin brands, which was sufficient to enable
positive victim identification. A more challenging task was
the identification of individuals after cremation and, more-
over, after processed cremains, as the dentition alters by
shrinkage and fragmentation. Nevertheless, the authors were
able to distinguish each individual in the study group posi-
tively under both circumstances (the cadavers were cremated,
and subsequently after XRF analysis, the cremains were
processed and re-measured). Once more, this study empha-
sised not only the wide applicability of (portable) XRF, now in
the domain of forensic odontology, but also the significant
value of restorative resins in victim identification, even after
cremation.
In contrast to these dedicated and bizarre applications,
X-ray spectrometry remains widely used in the more tradi-
tional application area of quality control of food and drugs.
Brazilian workers285 evaluated the elemental content of exotic
Brazilian tropical fruits by EDXRF. Consumer awareness
regarding balanced diets, encouraged the authors to determine
the nutritional composition (vitamins and minerals) in tropical
fruits. Using EDXRF, macro (Ca and K) and trace elements
(Br, Cu, Fe, Mn and Zn) were measured in 8 Brazilian tropical
fruits. The highest value of K amounted to 1.725 mg per 100 g,
whilst for Ca a value of 680 mg per 100 g was detected. The
trace elements ranged from 0.3 to 1.3 mg per 100 g for Br, 0.5
to 1.0 mg per 100 g for Cu, 3.9 to 11.4 mg per 100 g for Fe, 0.9
to 2.0 mg per 100 g for Mn and 0.6 to 1.5 mg per 100 g for Zn.
Comparative analysis with other tropical fruits indicated that
some of the Brazilian examples could be classified as rich
sources for these macro and trace elements. Mahawatte
et al.286 verified the quality of some Ayurvedic drugs by
measuring nineteen elements using EDXRF with a Mo target.
In all of the nineteen analysed samples Ca, Fe and K were
present, with a concentration ranging from 0.346 to 8.65%,
0.007 to 36.7% and 0.35 to 2.88%, respectively. The authors
were pleased to report that EDXRF provided a simple, non-
destructive and multi-element method to perform quality
control of drugs.
The distribution of Cd in plant material using a SEM-EDX
and the more sensitive m-SRXRF technique was studied by
Isaure et al.287 In addition, the chemical form was investigated
using Cd L-III-edge m-XANES. The results suggested that in
the roots, Cd was localised in vascular bundles and coordi-
nated to S ligands, whereas in the leaves, the Cd accumulation
was mainly focused in the trichomes (epidermal hair) and
mainly bound to O/N ligands, with only a minor fraction
bound to S-containing ligands. The fact that Cd mainly
accumulated in certain parts of trichomes was confirmed in
a comparable study of Hokura et al.288 An interesting con-
tribution was presented by Poussart et al.,289 showing the first
results for Ca from a ringless tree using the X-ray microprobe
synchrotron technique in order to estimate the tree’s age and
growth history. The Ca age model agreed within less than 2
years of radiocarbon age estimates and confirmed that the
cycles were seasonal. Moreover, the amplitude of the Ca
annual cycle significantly correlated with growth and the
annual Ca maxima correlated with the amount of dry season
rainfall. As these synchrotron measurements were fast, a
feasible analytical tool now seemed to be available for produ-
cing sufficient numbers of replicated multi-century tropical
dendrochemistry climate records. Serbian workers290 pre-
sented a rapid, simple and sensitive EDXRF procedure for
measuring W in tobacco plants after antiviral treatment with
12-tungstophosphoric acid and its compounds. Only 0.1 g of
dried plant material (tablets) was analysed instead of the usual
1 g. Using a 109Cd excitation source and 2000 s measurement
time, a detection limit for W of 15 mg kg�1 on a dry base could
be estimated. Quantitative analysis of different parts of the
1324 | J. Anal. At. Spectrom., 2007, 22, 1304–1332 This journal is �c The Royal Society of Chemistry 2007
treated plant together with the washings gave 94.5% recovery
of the applied W in different compound forms. Moreover, the
EDXRF results indicated that W was distributed both verti-
cally and horizontally throughout the tobacco plant.
Finally, readers still seeking additional clinical and biologi-
cal applications should refer to our companion Atomic Spec-
trometry Updates on Clinical and Biological Materials, Foods
and Beverages.3
9.7 Thin films and coatings
In recent years, considerable advances have been made in the
preparation of thin films, with industrial applications such as
protection, decoration and the fabrication of photoelectric
devices featuring extensively in the literature, where XRF
techniques have assisted in the understanding of the pro-
cesses involved. Transparent conducting oxides (TCOs) have
found extensive application in devices such as liquid crystal
displays, transducers and solar cells. ZnO is now regarded as
a promising material for TCOs due to its high transmission
over a wide spectral range and characteristics such as low
toxicity, relatively low cost and stability in reduced chemical
environments. Bacaksiz et al.291 studied spray pyrolysis
Cd1�xZnxO thin films prepared in an air atmosphere on glass
substrates at 250 1C and Zn-doped CdO films with high
optical transmittance for possible use as the window layer
of CdO/CdTe and Cd/CuInSe2 solar cells. The Kb/Ka X-ray
intensity ratio for elements on these types of film has been
reported in the past where it has featured in publications on
recent advances in solid state X-ray detectors, such as Si(Li)
and Ge detectors because it is considered a characteristic
quantity for each element in the film. In this paper, the
authors found that the Kb/Ka intensity ratio was changed
by the alloying effects in Cd1�xZnxO semiconductor thin
films as x varied from 0 to 0.60. The results were compared
with theoretical values anticipated. Dakhel292 continued his
investigations of manganese(III) thin films with a paper this
year on frequency-dependent conductivity in tri(acetylaceto-
nato) MnIII films of amorphous structure prepared by va-
cuum deposition on glass and Si(100) substrates. These films
were investigated for use as insulators for Al/insulator/Si(P)
metal-insulator-semiconductor (MIS) structures which were
characterised by the measurement of their capacitance and
ac-conductance as a function of gate voltage. The instru-
mental techniques used were XRF, XRD and optical absorp-
tion spectroscopy with the films analysed as-deposited and
annealed-in-vacuum. The work showed that tri(acetylaceto-
nato) MnIII films grown on Si(100) were a promising candi-
date for high-epsilon dielectric applications displaying
sufficiently high-8 value in the range 30–40. Yamaguchi et
al.293 characterised Cu(In, Ga)(S, Se)2 thin films prepared by
sequential evaporation from the ternary compounds Cu-
GaSe2, CuInSe2 and In2S3 for possible use as photovoltaic
devices. The XRF analysis showed Cu: (In + Ga): (S + Se)
atomic ratio in all the thin films was approximately 1:1:2. As
the In2S3/(CuGaSe2 + CuInSe2) mole ratio in the evaporat-
ing materials increased, the S/(S + Se) atomic ratio increased
from 0 to 0.6. XRD confirmed the prepared films had a
chalcopyrite structure and that the preferred orientation was
to the 112 plane. Putkonen and Niinisto294 investigated
atomic layer deposition of boron oxide thin films at room
temperature using BBr3 and H2O as precursors. Stoichiome-
try and possible impurities were determined by XRF with
other characteristics measured by XRD and time-of-flight
elastic recoil detection analysis. The as-deposited films were
amorphous and found to react readily with the atmosphere if
not protected by an alumina over-layer.
The electronic structure of Co-doped anatase (TiO2)
epitaxial thin films grown at different partial oxygen pressures
was investigated by Chang et al.295 using soft X-ray emission
spectroscopy. The resonantly excited Co L-2, L-3 emission
spectra of ferromagnetic Ti0.96Co0.04O2 samples for the
oxygen-deficient regime showed that the ratio of integral
intensities for Co L-2 and L-3 emission lines significantly
decreased with respect to non-magnetic samples in the oxygen
rich regime. This was due to L2L3M4,5 Coster–Kronig
transitions and suggested that the ferromagnetic samples had
n-type charge carriers and Co–Co bonds were dominant in
non-magnetic samples in the oxygen-rich regime. Electronic
structure calculations of the films also showed that the pre-
sence of free charge carriers and Co segregation play a crucial
role in strong ferromagnetism at room temperature. Jonnard
et al.296 showed that X-ray emission spectroscopy (XES)
induced by electrons and analysed with high spectral resolu-
tion by a wavelength dispersive Johann-type spectrometer was
a powerful technique for the study of Mo/Si multi-layers. The
optical properties of such Mo/Si periodic multi-layers depend
on the quality of the interfaces within the stacks. If the
inter-layers are formed as a result of a diffusion process at
the Mo-on-Si and Si-on-Mo interfaces, the optical
performance may be optimised. Several methods, such as
X-ray photo-electronic spectroscopy, Auger emission and
X-ray absorption are available to characterise these inter-
layers but are sensitive to the superficial 10 nm zone of the
sample because they use electrons as the detected particle.
However, XES induced by electrons is a more convenient
method, as the detected particles are photons that have a
much longer path in matter than electrons of the same energy.
Hence, information concerning electronic structure comes
from a thickness determined by the energy of the incident
electrons. In this way, it was possible to vary the electron
energy to probe all or only the first bi-layers in a stack.
Furthermore, information on the chemical state of the ele-
ments present at an interface of a periodic stack may be
obtained from analysis of the X-ray emission bonds. These
emissions involve valence electrons that are less tightly bound
and depend on the nature of the chemical bond formed in the
solid. By using a high resolution X-ray spectrometer, the
authors were able to observe the variation of the emission
band shape. They then evolved the shape of the Si Kbemission band (3p–1s transition) as a function of the chemical
environment of the Si atoms. A series of Mo/Si multi-layers
were studied where the thickness of the Si layers were 2 nm
and that of the Mo layers was 1, 2, 3 or 4 nm. The data
showed that the emission band from the Si atoms was
different from that of amorphous Si (a-Si) that should have
been observed if no diffusion process had taken place at the
interfaces. It was therefore possible to deduce the composition
This journal is �c The Royal Society of Chemistry 2007 J. Anal. At. Spectrom., 2007, 22, 1304–1332 | 1325
of the inter-layers and estimate their thickness as 0.4 � 0.1 nm
or 0.8 � 0.2 nm depending on the samples concerned.
In previous reviews, EDXRF has been reported as a means
of measuring the thickness of the cellulose nitrate layer of the
commonly used LR115 solid-state nuclear track detector
(SSNTD). Ng and Yu297 investigated whether the X-radiation
involved in the analytical process would induce degradation of
the cellulose nitrate. The nitrate functions were examined by
FTIR spectroscopy (at wavenumber 1598 cm�1) and the
glycosidic bonds (at 1146 cm�1) for the typical irradiation
time involved in the EDXRF analysis. It was pleasing to note
that no significant changes were reported for exposures up to
3000 s, which equated to the time required for 10 scans, far
longer than the time actually needed for a determination of the
cellulose nitrate-layer thickness. Therefore EDXRF remains
the technique of choice for the measurement of active layer
thickness of SSNTDs.
The literature during this review period continues to reflect
interest in nano-materials where it is inevitable that special
techniques are needed to handle and analyse these delicate
fabrications. Sachdeva et al.298 used an energy dispersive
spectrometer attached to an environmental scanning electron
microscope to investigate silver nano-particles formed by
chemical reduction of Ag+ in polyperfluorosulfonic acid
membranes with NaBH4. X-ray elemental mapping across
the thickness of the membrane indicated that Na+ and Ag+
were uniformly distributed in the membrane before reduction,
with the Ag concentration considerably increased after reduc-
tion. Furthermore, the nano-particles were formed only on the
membrane surface that was exposed to NaBH4 solution. The
average size of the nano-particles was found to be 15 � 3 nm.
Self diffusion of water, Na+ and Cs+ ions in the loaded
membrane was found not to affect the diffusion properties of
the membrane. The ion-exchange capacity and water uptake
were similarly unaffected. Azurdia et al.299 reported the use of
liquid feed flame pyrolysis to produce a series of nano-powders
along the CoOx–Al2O3 tie line. This general aerosol combus-
tion synthesis technique produced a wide range of lightly
agglomerated oxide nano-powders from aerosols of ethanol
solutions of alumatrane, Al(OCH2CH2)3N, and a cobalt pre-
cursor made by reacting Co(NO3)2 � 6H2O crystals with pro-
pionic acid. Nine samples were prepared and studied by XRF,
BET, SEM, high resolution TEM, XRD, TGA and FTIR.
From the wealth of data produced, the powders were reported
to consist of single crystal particles o40 nm in diameter and
with a specific surface area of 20–60 m2 g�1. A gradual change
in the XRD powder patterns from delta Al2O3 to Co3O4 was
seen with a cobalt aluminate spinel phase that had not
previously been published in phase diagrams. High cobalt
content samples exhibited a sharp mass-loss that was attrib-
uted to the decomposition of Co3O4 to CoO. Magnesia is an
accepted additive to BaTiO3 powder for use in the manufac-
ture of multi-layer ceramic capacitors (MLCC). Kim et al.300
investigated a nano-coating process for the production of a
MgO shell layer onto BaTiO3 core powder. Several deposition
reaction routes were examined with a magnesium nitrate–urea
system reported to be satisfactory. The core shell morphology
was characterised by SEM and TEM, whereas the composi-
tion of the shell layer was determined by ICP-AES and XRF.
Those embarking on investigations of coating samples may
be interested in a paper by Han et al.,301 who calculated the
fluorescence intensity enhanced by scattering effects for coat-
ing samples based on the familiar fundamental parameter
models. They calculated the contribution of secondary en-
hancement due to scattered radiation from the same layer or
between layer and substrate and the primary fluorescence that
was scattered into the direction of a detector by atoms in a
layer or substrate. Using a hypothetical Zn coating on an
infinite Fe substrate the contributions from these different
scattering effects were shown to relate to coating thickness
and were up to several percent of the primary fluorescent
intensity.
9.8 Chemical state, speciation and crystal characterisation
In this section of the review we consider studies on informa-
tion gained from X-ray absorption spectroscopy (XAS) based
on the excitation of electrons from the deep core levels of an
atom by the absorption of an X-ray photon. The XAS
spectrum is divided into two parts: X-ray absorption near
edge structure (XANES) and extended X-ray absorption fine
structure (EXAFS). XANES extends from a few eV below the
absorption edge of an element to about 40–50 eV above the
edge, whereas EXAFS provides information from 50–1000 eV
above the edge. Goraieb et al.302 used both conventional XRF
and XAS for the characterisation of titania grafted onto the
surface of silica used as a support medium in HPLC. The TiO2
layer is known to have the same chemical properties as the
bulk crystalline phase when trapped on a mechanically resis-
tant silica matrix and these workers analysed the treated
support medium before and after extensive use in reversed-
phase HPLC. The XRF data indicated the formation of a
complete 2:1 monolayer whereas XAS suggested the presence
of more than one structure of titanium oxide after use.
Pinakidou et al.303 studied EXAFS spectra of Fe in a series
of vitrified Fe and Pb rich industrial waste samples that
contained toxic ash. XRF mapping in combination with
m-XAS of samples containing 50% and 60% ash demonstrated
that annealing at temperatures above 600 1C induced loss of
homogeneity and the formation of Fe rich micro-crystalline
‘‘islands’’. It is pleasing to note that information available
from the study of absorption spectra is now appreciated in the
wider X-ray community and finding application outside
academe.
An alternative approach to EXAFS and XANES is to study
the radiative Auger spectra generated by photon excitation.
Raju et al.304 gathered K X-ray emission spectra to study the
Ka hyper-satellite, KbL1 and Kb5 satellites, as well as KMM
radiative Auger emissions of elements from K to Mn in the
periodic table. Ka hyper-satellite lines are the weak lines that
appear on the high energy side of the diagram lines when an
atom is doubly ionised in the K shell and if these holes are
filled by transitions from the outer shells. Such transitions
originate from L, M, N. . .shells and are known as Ka, Kb,Kg. . .hyper-satellites, respectively. If ionisation occurs in just
the K shell and all the other shells are filled, the resulting
hyper-satellites are denoted as KahL0, but if there is simulta-
neous ionisation in the L shell, this de-excitation of the atom
1326 | J. Anal. At. Spectrom., 2007, 22, 1304–1332 This journal is �c The Royal Society of Chemistry 2007
gives rise to satellites of hyper-satellites denoted as KahLn or
Ka2Ln, where n is the number of holes in the l shell. Using a
conventional WDXRF with LiF200 and LiF220 crystals, the
authors investigated the Z-dependence of the energy shift and
relative intensity of these weak lines (humps and bumps) with
respect to their conventional characteristic lines. Only energy
shifts were examined in the KMM radiative Auger spectra. All
the data were compared with the available predictions. To
assist in the understanding and identification of these weak
KMM spectra, the authors assigned the transitions as
K–M1M2 (3p), K–M1M2 (1p) and K–M1M2 (1s). It is thought
that studies such as these may take time to find practical
application.
Whilst polarised EDXRF spectrometers are appreciated for
their enhanced sensitivity when compared with WDXRF
configurations, the resolution offered by the latter may be
used to good effect by those interested in studies of peak shape
and profiles. Deluigi and colleagues305 proposed an index for
chemical state analysis based on information from such spec-
tra following their studies on the Kb emissions of Cr in
different compounds. Higher resolution measurements from
the Kb1,3 line were also obtained using a spectrometer based
on a back diffracting crystal analyser with spherical focusing
and excitation from monochromatic synchrotron radiation.
Kb1,3 line shifts were seen from metallic Cr to higher energies
for CrIII and to lower energies for CrVI. The authors also
reported that the natural width of the Kb1,3 line, the ionisationenergy of the 3p orbital of Cr and the relative intensities of Kband Kb2,5 lines increased as the oxidation state increased. Two
authors from the same team in Argentina306 also studied the
Kb profiles from six different oxidation states of sulfur. The
structural changes were observed using WDXRF and showed
good agreement with theoretical data calculated using mole-
cular orbital theory available in the literature. Han et al.307
studied different valency states of Mn and Fe in a Chinese
language paper. They used a spectral processing software
programme, ‘‘Peakfit’’ and found that the Kb lines were
appropriate for Mn whereas the L lines were better than the
K lines for studies of the chemical state of Fe. They also used a
conventional wavelength dispersive spectrometer.
10 Abbreviations
AD Anno Domini
AF Antifouling
ALS Amyotrophic lateral sclerosis
APD Avalanche photodiode detector
APDC Ammonium pyrrolidine dithiocarbamate
ASV Anodic stripping voltammetry
BET Brunauer, Emmett and Teller surface
area analysis
BC Before Christ
CCD Charge coupled detector
CFC Close faced cassette
CML Chronic myelogenous leukaemia
CMOS Complementary metal oxide semiconductor
CRM Certified reference material
D Dimensional
(continued )
DePMOS Drain extended p-channel
metal oxide semiconductor
EDXRF Energy dispersive X-ray fluorescence
EPMA Electron probe microanalysis
EPR Electron Paramagnetic Resonance
EPA Environmental Protection Agency
ESEM Environmental scanning electron
microscope
ESRF European synchrotron radiation facility
EXAFS Extended X-ray absorption fine structure
FAAS Flame atomic absorption spectrometry
FTIR Fourier transform infrared spectroscopy
FP Fundamental parameters
HCA Hierarchical cluster analysis
HPLC High-performance liquid chromatography
IAEA International Atomic Energy Agency
ICP-AES Inductively coupled plasma-atomic
emission spectrometry
ICP-MS Inductively coupled plasma-mass
spectrometry
ICP-OES Inductively coupled plasma-optical
emission spectroscopy
IDMS Isotope dilution mass spectrometry
IED Iminodiacetate extraction disc
INAA Instrumental neutron activation analysis
IOM Institute of Occupational Medicine
LNLS Laboratorio National de Luz Synchrotron
MIMs Multilayer interference mirrors
MLCC Multilayer ceramic capacitors
MPI Max Planck Institute
MS Mass spectrometry
NAA Neutron activation analysis
NIST National Institute of Standards and
Technology
PCA Principle component analysis
PIXE Particle induced X-ray emission
PM Particulate matter
PTB Physikalisch-Technische Bundesanstalt
PTFE Polytetrafluoroethylene
PVC Poly(vinyl chloride)
PXRF Portable X-ray fluorescence
RCA Recycled concrete aggregates
REE Rare earth element(s)
RM Reference material
RoHS Restriction on Hazardous Substances
QC Quality control
QXAS Quantitative X-ray analysis system
SDD Silicon drift detector
SEM Scanning electron microscopy
SIMS Secondary ion mass spectrometry
SR Synchrotron radiation
SRM Standard reference material
SRXRF Synchrotron radiation X-ray
fluorescence
SR-TXRF Synchrotron radiation-total
reflection X-ray fluorescence
SSNTD Solid-state nuclear track detector
This journal is �c The Royal Society of Chemistry 2007 J. Anal. At. Spectrom., 2007, 22, 1304–1332 | 1327
(continued )
STJ Superconducting tunnel junctions
TCO Transparent conducting oxides
TEM Transmission electron microscope
TES Transition-edge-sensor
TGA Thermo-gravimetric analysis
TXRF Total reflection X-ray fluorescence
USA United States of America
UV-VIS Ultraviolet–visible spectroscopy
WDXRF Wavelength dispersive X-ray
fluorescence
WEEE Waste Electrical and Electronic
Equipment
XAFS X-Ray absorption fine structure
spectroscopy
XANES X-ray absorption near edge structure
XAS X-ray absorption spectroscopy
XES X-ray emission spectroscopy
XRD X-ray diffraction
XRF X-ray fluorescence
Z Atomic number
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