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Quantitative analysis of silicate certified reference materials by LA-ICPMSwith and without an internal standard

Joel E. Gagnon,*a Brian J. Fryer,a Iain M. Samsona and Anthony E. Williams-Jonesb

Received 31st January 2008, Accepted 10th July 2008

First published as an Advance Article on the web 28th August 2008

DOI: 10.1039/b801807n

Quantitative analysis of silicate minerals by laser ablation-inductively coupled plasma mass

spectrometry (LA-ICPMS) typically has relied on the use of an internal standard estimated from

mineral stoichiometry or obtained using an alternative analytical technique (e.g., electron microprobe

(EMP)). Major, minor and trace element analysis of silicate certified reference materials (CRMs) can be

conducted by LA-ICPMS without using an internal standard by analyzing for a comprehensive list of

elements, converting the elements to equivalent oxide concentrations, scaling the oxides to 100%, and

converting the scaled oxide concentrations back into element concentrations. This method

demonstrates that quantitative element concentrations can be obtained from silicate CRMs having

a wide range of compositions without using an internal standard and, in general, results obtained using

this method are equally or more accurate than those obtained using any one of three elements (Si, Ca or

Fe) as internal standards. The approach expands the application of LA-ICPMS to the analysis of

unknown silicate minerals.

Introduction

Quantitative analysis of silicates by laser ablation inductively-

coupled plasma mass spectrometry (LA-ICPMS) typically has

been limited to the determination of minor and trace element

concentrations using an internal standard. Two approaches typi-

cally used to estimate the concentration of the element that is used

as the internal standard are: (1) the proportion of an element in

an ‘ideal’ mineral formula (i.e., stoichiometry), or (2) another

analytical method (e.g., EMP). Alternative methods of standard-

ization, such as simultaneous addition of desolvated liquid stan-

dards,1,2 also have been used. These approaches require that the

concentrationof at least one element (i.e., the internal standard)be

estimated independently for each sample, and which add a degree

of complexity to LA-ICPMSanalyses, or potentially contribute to

problematic molecular ion interferences (e.g., oxides, hydrides),

which may prevent quantitative analysis of some elements.2

Quantitative analysis of silicateminerals of unknown composition

(i.e., without using internal standards) often is required when

conducting geological investigations. Itwould, therefore, beuseful

to have a method of determining element concentrations in

materials of unknown composition using LA-ICPMS that is

simple, does not necessarily rely on internal standards, and does

not suffer from problematic interferences.

This paper presents an oxide scaling method for conducting

quantitative major, minor and trace element analyses of silicates

by LA-ICPMS that does not require the use of an internal

standard. The applicability of the technique is demonstrated by

the analysis of six synthetic silicate certified reference materials

aDepartment of Earth & Environmental Sciences, University of Windsor,Windsor, Ontario, Canada. E-mail: jgagnon@uwindsor.ca; Fax:+1-519-973-7081; Tel: +1-519-253-3000bDepartment of Earth & Planetary Sciences, McGill University, Montreal,Quebec, Canada; Fax: +1-514-398-4680; Tel: +1-514-398-6767

This journal is ª The Royal Society of Chemistry 2008

(CRMs) (NIST 610, NIST 612, NIST 614, BCR-2G, BHVO-2

and BIR-1). The accuracy of the technique is evaluated by

comparing the results of analyses obtained for: (1) NIST 610

(treated as an unknown or ‘blind’ sample) with published values,

and (2) all six reference materials obtained without using an

internal standard with those obtained using three different

internal standards (Si, Ca and Fe). The precision of the oxide

scaling technique is evaluated by conducting ten replicate anal-

yses of each of the reference materials and calculating the

standard deviation of the mean (SD). Finally, the results of the

analyses of the CRMs, calculated using the most accurate stan-

dardization technique obtained using NIST 610, are presented.

These data indicate that quantitative analysis of unknown

silicates can be obtained with acceptable accuracy and without

using an internal standard. Furthermore, tentative values are

proposed for elements contained in the silicate CRMs for which

certified, reference, or information (CRI) values were not previ-

ously available.

Certified reference material analysis

Sample material and preparation

The CRMs included in this study were obtained from the

National Institute of Standards and Technology (NIST) and the

United States Geological Survey (USGS). The NIST reference

materials were synthesized using a silicate glass matrix and

contain approximately 450 ppm (NIST 610), 40 ppm (NIST 612),

and 1 ppm (NIST 614) of a wide range of trace elements. The

USGS reference materials are silicate glasses prepared from

natural basaltic materials obtained from type localities in Oregon

(BCR-2), Hawaii (BHVO-2), and Iceland (BIR-1).

The reference materials, as obtained from NIST and USGS,

were cut into approximately 4 mm � 4 mm � 2 mm wafers using

a low speed diamond saw (Buehler Isomet�) and cleaned by

J. Anal. At. Spectrom., 2008, 23, 1529–1537 | 1529

Table 2 ICPMS instrumentation and operating conditions

Manufacturer: ThermoElectron�

Model: X7�

Detector type: ETP� dual mode (pulse and analogue)Dynamic range: �1 � 109 integrated counts s�1 (ICPS)Sensitivity (sol.): �350 � 106 ICPS ppm�1

Cone type: High performance interface (HPI)Plasma conditions: StandardInstrument tuning: Lens & torch position: manual tune

RF power: 1200 W

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sonicating them for 15 min in MilliQ� water. The fragments were

bonded to a single glass slide with approximate dimensions of 27

mm � 46 mm � 1 mm using water-soluble glue (Weldbond�),

and were stored in covered plastic Petri dishes within a fume

hood until LA-ICPMS analyses were conducted. Immediately

before being introduced into the laser cell, the tops of the CRM

fragments were wiped with ultrapure ethanol and blown dry with

clean, compressed air. The slide was then placed in the laser

sample cell under an Ar gas flow.

Resolution: Standard-125, High-145Ar cool gas: 14 L min�1

Ar auxiliary gas: 0.9 L min�1

Ar nebulizer gas: 1.04 L min�1

Quadrupole bias: 0.5Hexapole bias: �1.5

Data acquisition: Dwell time/mass: 10 msMasses analyzed: 81Elements quantified: 64Mass sweeps/acquisition: 250

LA-ICPMS instrumentation

The LA-ICPMS analyses were conducted in the Great Lakes

Institute for Environmental Research at the University of

Windsor, Windsor, Ontario, Canada. The laser ablation system

comprised a non-homogenized Continuum Surelite I� solid state,

266 nm Nd:YAG laser, an Oriel� optical bench, an Olympus�

BX-51 polarizing light microscope equipped with a Prior�

computer-controlled stage, and miscellaneous devices for beam

size and power manipulation and attenuation (see Table 1 and

Gagnon et al.3 for details).

Laser-generated sample aerosols were transported from the

ablation cell directly to the torch of a ThermoElectron� X7�

ICPMS by routing all of the ICPMS nebulizer gas flow (�1.04 L

min�1) through the sample cell. A summary of the ICPMS

specifications and operating conditions used in this study are

presented in Table 2.

Table 3 Measured masses and quantified elements

Masses measured (81) Elements quantified (64)

Experimental conditions and data acquisition

The high sensitivity of current ICPMS instruments can make it

difficult to determine elements that occur in high concentrations

(i.e., weight%) in silicates without count rates exceeding the

dynamic range of the instrument detector. Tunable mass reso-

lution enables the ThermoElectron� X7� ICPMS to conduct

simultaneous quantitative laser ablation analysis of element

concentrations ranging from ppb to weight percent. The high

mass resolution setting is manually adjusted during the pre-

experiment instrument setup to ensure that relatively abundant,

monoisotopic major elements (e.g., Na) are measured exclusively

using the pulse mode of the detector. This ensures that the

dynamic range of the detector will not be exceeded and eliminates

any imprecision that may result from the cross-calibration

between detector modes if data are collected in one mode

Table 1 LA system specifications and operating conditions

Manufacturer: Continuum�

Model: Surelite� IFrequency: 20 HzWavelengths: Fundamental: 1064 nm

Output: 266 nmLamp voltage: Maximum: 1.3 kV

Experiment: 1.12 kVPulse energy(before focusing):

Maximum: 2 mJ pulse�1 (100% power)Experiment: �0.8 mJ pulse�1 (�40% power)

Iris: 1 mm diameterObjective lens: 10�Spot size: 20 mmTraverse rate: 5 mm s�1

1530 | J. Anal. At. Spectrom., 2008, 23, 1529–1537

(e.g., analogue) and initial instrument calibration is carried out in

another mode (e.g., pulse).

The silicate CRMs were analyzed for a comprehensive list of

isotopes in order to improve the accuracy of the concentration

data calculated without using an internal standard (i.e., by oxide

scaling, see below). A total of 81 masses, representing all major

elements and the majority of the minor and trace elements

present in the CRMs, as well as various matrix and molecular

ions necessary to assess ICPMS tuning conditions (e.g., UO),

were measured. Through a combination of selecting low abun-

dance isotopes (e.g., 29Si) and selectively tuning the high mass

resolution of the ICPMS, the concentrations of 64 elements were

determined during a single analysis. The list of masses that were

measured, and the elements that were quantified during each

analysis, are presented in Table 3.

Five experiments, each consisting of 16 analyses, were con-

ducted. Each experiment included two replicate analyses of each

of the six silicate glass CRMs, and these analyses were preceded

and followed by two replicate analyses of NIST 610 (i.e., the

external calibration standard). The sequence of analysis was

NIST 610, NIST 612, NIST 614, NIST 610, BCR-2, BHVO-2,

7Li, 9Be, 11B, 23Na, 25Mg, 27Al,29Si, 31P, 33S, 39K, 43Ca, 44Ca,45Sc, 47Ti, 51V, 52Cr, 53Cr, 55Mn,57Fe, 59Co, 60Ni, 62Ni, 65Cu, 66Zn,68Zn, 69Ga, 72Ge, 75As, 77ArCl,82Se, 83Kr, 85Rb, 86Sr, 88Sr, 89Y,90Zr, 93Nb, 95Mo, 103Rh, 105Pd,107Ag, 110Cd, 111Cd, 115In, 118Sn,120Sn, 121Sb, 133Cs, 136Ba, 137Ba,139La, 140Ce, 141Pr, 146Nd, 147Sm,153Eu, 155Gd, 156CeO, 157Gd,159Tb, 163Dy, 165Ho, 166Er, 169Tm,172Yb, 175Lu, 178Hf, 181Ta, 182W,185Re, 195Pt, 197Au, 205Tl, 206Pb,207Pb, 208Pb, 209Bi,220Background, 232Th, 238U and254UO

Li, Be, B, Na, Mg, Al, Si, P, K,Ca, Sc, Ti, V, Cr, Mn, Fe, Co,Ni, Cu, Zn, Ga, Ge, As, Se, Rb,Sr, Y, Zr, Nb, Mo, Rh, Pd, Ag,Cd, In, Sn, Sb, Cs, Ba, La, Ce,Pr, Nd, Sm, Eu, Gd, Tb, Dy,Ho, Er, Tm, Yb, Lu, Hf, Ta, W,Re, Pt, Au, Tl, Pb, Bi, Th and U

This journal is ª The Royal Society of Chemistry 2008

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BIR-1, and NIST 610. The five experiments resulted in a total of

80 analyses, comprising 10 replicates of each reference material

(including NIST 610), that were being treated as unknowns,

and 20 additional analyses of NIST 610, which were used as the

external calibration standard for the determination of the

instrumental drift and element sensitivity factors (SFs) (i.e.,

integrated counts s�1 ppm�1 ¼ ICPS ppm�1). All five experiments

were conducted during a single operating session to ensure that

relatively constant instrument operating and tuning conditions

were used throughout the study. The quadrupole analyzer of

the ICPMS was mass calibrated, the detector plateau was

determined, and the ICPMS was tuned to simultaneously achieve

maximum sensitivity and minimal formation of oxides (e.g., UO/

O < 0.1%) at the beginning of the operating session.

Each analysis consisted of collecting 1min of data on combined

instrument and gas background, traversing the reference material

with the laser beam at a constant rate (5 mms�1) using a computer-

controlled, programmable stage for a duration of 2.5 min, and

then collecting an additional 0.5 min of background data.

Table 4 List of oxide formulae and cation mole fractions

Oxideformula

Cation molefraction

Oxideformula

Cation molefraction

Oxideformula

Cation molefraction

Li2O 0.4646 As2O3 0.7574 Sm2O3 0.8624BeO 0.3603 SeO 0.8315 Eu2O3 0.8636B2O3 0.3106 Rb2O 0.9144 Gd2O3 0.8676Na2O 0.7419 SrO 0.8456 Tb2O3 0.8688MgO 0.6030 Y2O3 0.7874 Dy2O3 0.8713Al2O3 0.5293 ZrO2 0.7403 Ho2O3 0.8730SiO2 0.4674 Nb2O5 0.6990 Er2O3 0.8745P2O5 0.4364 Mo2O3 0.7999 Tm2O3 0.8756K2O 0.8302 Rh2O3 0.8109 Yb2O3 0.8782CaO 0.7147 PdO 0.8693 Lu2O3 0.8794Sc2O3 0.6520 Ag2O 0.9310 HfO2 0.8480TiO2 0.5993 CdO 0.8754 Ta2O5 0.8190V2O5 0.5602 In2O3 0.8271 WO3 0.7930Cr2O3 0.6842 SnO 0.8812 ReO2 0.8534MnO 0.7745 Sb2O3 0.8354 PtO 0.9242FeO 0.7773 Cs2O 0.9432 Au2O 0.9610CoO 0.7865 BaO 0.8957 Tl2O3 0.8949NiO 0.7858 La2O3 0.8527 PbO 0.9283CuO 0.7989 Ce2O3 0.8538 Bi2O3 0.8970ZnO 0.8035 Pr2O3 0.8545 ThO2 0.8788GaO 0.8134 Nd2O3 0.8574 UO2 0.8815GeO2 0.6942

Data reduction

Data selection and correction

Integration regions for each certified reference material analysis

were selected from the time-resolved data (i.e., ICPS/time) using

ThermoElectron� PlasmaLab� software. One integration region

was selected from the approximately 1 min of pre-ablation

background, and one region was selected from the stable portion

of the signal corresponding to the approximately 2.5 min of

CRM ablation. The output data (average ICPS) were transferred

to commercial spreadsheet software, which was used to convert

the ICPS data into concentration units (ppm).

The CRM ablation signal was corrected for instrument

background by subtraction.4 Background-corrected data were

then corrected for instrumental drift using two different proce-

dures. Where NIST 610 was treated as an unknown, drift

corrections were calculated based on the first and last two

samples (i.e., external calibration standards) in each experiment.

To improve analytical accuracy for the remaining reference

materials, each experiment was divided into two halves and the

two NIST 610 analyses conducted in the middle of the experi-

ment were used to calculate separate instrumental drift correc-

tions for the first and second halves of the experiment.

Drift corrections were performed by constructing matrices of

sensitivity factors for each element based on the normalized

sensitivities calculated from the external calibration standard

using the procedure of Longerich et al.4NIST 610 was used as the

external calibration standard because it has the greatest number

of certified, reference or information values of all the CRMs

analyzed. Application of the NIST 610 elemental sensitivity

factors to the other reference materials enabled calculation of the

greatest number of elements for the remaining CRMs, including

some elements currently without published CRI values. Element

concentrations uncorrected for differences in the amount of

unknown sample ablated relative to NIST 610 (i.e., ablation

sensitivity correction) were calculated for each sample by dividing

the average ICPS by the corresponding element sensitivity

factor.4 Conversion of the uncorrected element concentrations to

This journal is ª The Royal Society of Chemistry 2008

corrected (i.e., quantitative) concentrations was accomplished by

determining scaling factors and converting the uncorrected

element concentrations to scaled element concentrations using

either: (1) an internal standard, or (2) by oxide scaling.

Internal standard method

For calculations using an internal standard, scaling factors were

calculated by dividing the unscaled element concentrations

obtained for the internal standard element (e.g., 29Si, 44Ca or 57Fe)

by the CRM certified, reference, or information value. The

unscaled concentrations for all other elements in the sample were

subsequently converted to scaled (i.e., quantitative) element

concentrations by dividing by the appropriate scaling factor.4

The resulting data are reported in ppm concentration units.

Oxide scaling method

CScaled ¼���X CRaw

6Oxide

��1000000

�*CRaw

�*6Oxide (1)

Element concentrations were calculated without an internal

standard using an oxide scaling method. This consisted of

converting the uncorrected element concentrations (CRaw) into

uncorrected oxide concentrations by dividing by the mass

fraction of the cation in the oxide formula (6Oxide), scaling to

100% (i.e., 1 000 000 ppm), and converting the scaled oxide

concentrations back to corrected element concentrations

(CScaled) using eqn (1).

The oxide formulae used in calculating the cation mole frac-

tions are presented in Table 4. The CRMs included in this study

comprise silicate glass and cations present in the CRMs are

coordinated with O and Si, making oxide scaling a viable means

of obtaining quantitative concentration data without using an

internal standard.

J. Anal. At. Spectrom., 2008, 23, 1529–1537 | 1531

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An oxide scaling approach to quantification was previously

used on silicate reference materials by Halicz & Gunther.2 The

authors used a desolvated solution standard to determine

a scaling factor for Ca, which was then applied to all other

elements. A comprehensive list of elements was not used

(e.g., K), which prevented direct oxide scaling of all elements

independently. The key differences between the approach of

Halicz & Gunther2 and the approach presented in this study are:

(1) a more extensive analyte list is used, which enables determi-

nation of all element abundances simultaneously by direct

scaling of oxide concentrations without using a single scaling

factor obtained from a single element (e.g., Ca) for all elements,

(2) a desolvated standard solution was not used for calibration of

an internal standard (i.e., Ca), which prevents the formation

of molecular ion interferences that may prevent quantification of

certain elements (e.g., Cu),2 and (3) all elements were scaled

independently, without applying a single scaling factor deter-

mined for a single element (e.g., Ca).2

Limit of detection calculation

Following calculation of the element concentrations, all results

were filtered for the limit of detection (LODRaw) using the

method of Longerich et al.4 The LODRaw were then adjusted by

multiplying them by the scaling factors determined using either

an internal standard or by oxide scaling to obtain scaled LODs

(LODScaled).

Results and discussion

NIST 610

Concentration data for ten analyses of NIST 610 (treated as

unknowns) calculated using Si, Ca and Fe as internal standards

and by oxide scaling are presented in Table 5. Certified, reference

or information values for all of the CRMs were compiled from

a number of sources.4–28 The differences between the measured

element concentrations and the certified, reference, or informa-

tion values (expressed as percentages) are included in the table.

The method of standardization yielding the lowest percentage

difference between the measured element concentration and the

certified, reference or information value (i.e., most accurate) is

indicated in bold italics.

The measured NIST 610 concentrations are generally different

from the certified, reference, or information values despite using

NIST 610 as the external calibration standard (Table 5). There-

fore, the differences between the measured and certified,

reference or information values must result from analytical

imprecision because the calibration standard was 100% matrix-

matched to the unknowns (i.e., NIST 610) and all other variables

were constant throughout the 5 experiments.

No one method of standardization (i.e., use of an internal

standard or oxide scaling) consistently produced the most

accurate results for all elements. Deviation from the NIST

610 certified, reference, or information values (i.e., analytical

error) of less than approximately �5% was observed for all

64 elements using all 4 different standardization methods

(i.e., Si, Ca, Fe internal standards and oxide scaling).

The analytical error varied according to the standardization

method used, with Fe yielding the lowest and Ca yielding the

1532 | J. Anal. At. Spectrom., 2008, 23, 1529–1537

highest analytical errors for the greatest number of elements.

Average analytical errors (i.e., errors resulting from averaging

data obtained using all 4 standardization methods) were less than

approximately �2% for all elements except Rb, Pd, Cd, Sb, Pt,

Au, Tl, Bi and Th.

Using Fe as an internal standard resulted in the most accurate

results for the greatest number (39) of elements (Li, Be, B, Mg,

Al, Zn, Ge, As, Se, Rh, Pd, Ag, Cd, Sb, Ba, La, Ce, Pr, Nd, Sm,

Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Pt, Au, Tl,

Pb, Bi and Th). Using Si as an internal standard resulted in the

most accurate results for 12 elements (Na, Ca, Ti, Co, Ni, Cu,

Ga, Y, Zr, Nb, Mo and U). Scaling the oxide concentrations

resulted in the most accurate results for 7 elements (Si, P, Sc, Mn,

Fe, Sr, and Sn). Using Ca as an internal standard resulted in the

most accurate results for only 6 elements (K, V, Cr, Rb, In and

Cs). Calculation of element concentrations using oxide scaling

provided better accuracy for more elements than using Si or Ca

as an internal standard. The relative accuracy notwithstanding,

even using the least accurate element (i.e., Ca) as the internal

standard produced relatively small analytical errors of less than

approximately � 3% for the majority of elements (56 of 64).

Other certified reference materials

Concentration data for NIST 612 and NIST 614 are presented in

Table 6 and concentration data for BCR-2G, BHVO-2 and BIR-

1 are presented in Table 7. Concentrations for NIST 612 and

614 were calculated using only Si and Ca as internal standards

and by oxide scaling because Fe was not detected at concentra-

tions in excess of the LODs for these reference materials.

Concentrations for BCR-2G, BHVO-2 and BIR-1 were calcu-

lated using Si, Ca and Fe as internal standards, and by oxide

scaling. The method of standardization yielding the lowest

percentage difference between the measured element concentra-

tion and the CRI value is indicated as a subscript.

As with NIST 610, measured concentrations for the five

certified reference materials (NIST 612, NIST 614, BCR-2G,

BHVO and BIR-1) are generally different from the certified,

reference or information values (Tables 6 and 7) and one method

of standardization did not consistently produce the most accu-

rate results for all elements determined.

Average analytical errors were less than approximately �10%

for the majority of elements included in the analysis of NIST 612.

Thirteen elements (B, Mg, P, Sc, Ti, As, Nb, Ag, In, Sb, Er, Tm,

and Th) had average analytical errors greater than approxi-

mately �10%. Using Ca as an internal standard resulted in the

most accurate results for the greatest number (35) of elements

(Mg, P, Sc, Ti, V, As, Rb, Y, Zr, Nb, Mo, Ag, Cd, In, Sn, Sb, Cs,

Ba, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ta, Au,

Pb, Th and U). Scaling the oxide concentrations resulted in the

most accurate results for 17 elements (Al, Si, Ca, Cr, Mn, Co, Cu,

Ga, Sr, La, Eu, Hf, W, Re, Pt, Tl and Bi). Using Si as an internal

standard resulted in the most accurate results for 9 elements

(Li, Be, B, Na, Ni, Zn, Ge, Rh, Pd and Re).

Average analytical errors were less than approximately �10%

for the majority of elements included in the analysis of NIST 614.

Nineteen elements (Li, B, Ti, Zn, Ga, Ge, Rb, Y, Pd, Cd, In, Sn,

Er, Tm, Yb, Lu, Pt, Au and Pb) had average analytical errors

greater than approximately �10%. Using Ca as an internal

This journal is ª The Royal Society of Chemistry 2008

Table 5 Calculated concentrations–NIST 610a

Element CRI

29Si internal 44Ca internal 57Fe internal Oxide scaled

CScaled SD % CScaled SD % CScaled SD % CScaled SD %

Li 4855 491 4.37 1.34 497 10.4 2.54 489 9.76 0.78 491 4.61 1.24Be 4665 471 3.15 1.07 476 7.70 2.18 468 6.84 0.44 470 2.94 0.96B 3565 359 2.32 0.72 363 6.35 1.85 356 5.40 0.10 358 2.28 0.61Na 99 4005 98 900 595 0.49 100 000 2290 0.75 98 400 2010 1.01 98 800 688 0.59Mg 4655 467 1.83 0.54 473 7.40 1.65 465 7.59 0.05 467 1.33 0.43Al 10 8005 10 800 39.1 0.38 11 000 184 1.51 10 800 176 0.20 10 800 32.3 0.27Si 330 0005 330 000 0 0 334 000 6200 1.17 328 000 5770 0.55 330 000 610 0.10P 3435 343 1.77 0.06 347 6.91 1.25 341 5.42 0.53 343 1.85 0.04K 4865 482 7.80 0.78 487 5.14 0.13 479 7.01 1.50 482 7.10 0.91Ca 79 0005 78 400 1480 0.81 79 000 0 0 77 700 985 1.60 78 300 1340 0.94Sc 4415 442 5.57 0.18 446 3.11 1.12 439 4.24 0.55 441 4.79 0.06Ti 4345 434 5.22 0.09 438 4.41 0.87 430 4.09 0.83 433 4.60 0.22V 4425 436 5.55 1.47 440 3.74 0.53 432 4.82 2.18 435 4.86 1.59Cr 4055 401 4.94 1.07 405 4.56 0.10 398 2.61 1.82 400 4.34 1.19Mn 433.36 434.2 4.75 0.20 438.5 5.35 1.21 431.0 4.10 0.52 433.6 4.15 0.08Fe 4586 462 7.87 0.86 466 6.21 1.79 458 0 0 461 7.21 0.73Co 4055 404 4.58 0.26 408 5.04 0.74 401 3.03 1.00 403 4.02 0.38Ni 458.76 457.4 4.56 0.28 462.1 6.18 0.74 454.1 4.05 1.00 456.9 3.97 0.40Cu 4305 429 4.48 0.33 433 5.00 0.67 426 4.30 1.04 428 3.85 0.45Zn 4565 461 5.52 1.00 465 4.74 1.98 458 6.97 0.33 460 4.81 0.87Ga 4385 438 4.49 0.09 442 5.56 0.93 435 5.32 0.77 437 4.00 0.21Ge 4265 430 4.46 1.03 435 5.70 2.06 427 4.18 0.31 430 3.94 0.91As 3175 320 3.32 1.08 324 3.99 2.11 318 3.50 0.38 320 2.87 0.96Se 1095 110 1.71 0.87 111 1.51 1.83 109 1.04 0.08 110 1.58 0.74Rb 425.76 415.9 4.37 2.30 420.1 5.20 1.31 413.1 5.28 2.96 415.4 3.81 2.42Sr 515.56 516.0 4.03 0.10 521.6 7.85 1.17 512.5 5.78 0.58 515.4 3.54 0.02Y 4505 448 3.53 0.50 452 6.33 0.56 445 5.33 1.16 447 3.03 0.61Zr 4405 439 3.34 0.32 443 6.84 0.76 436 5.71 0.97 438 3.01 0.43Nb 4195 419 3.14 0.06 423 6.25 1.02 416 5.10 0.72 418 2.75 0.17Mo 4107 409 3.52 0.26 413 6.48 0.82 406 4.46 0.94 408 3.18 0.37Rh 1.38 1.3 1.01 0.75 1.3 0.03 1.87 1.3 0.02 0.07 1.3 0.01 0.64Pd 1.18 1.1 0.03 3.48 1.2 0.04 4.88 1.1 0.03 2.90 1.1 0.03 3.39Ag 2395 242 2.68 1.19 244 3.40 2.23 240 3.61 0.53 242 2.36 1.07Cd 2595 265 3.68 2.40 268 4.65 3.47 264 5.20 1.78 265 3.43 2.28In 4415 438 4.46 0.59 443 6.27 0.44 436 7.55 1.19 438 4.00 0.71Sn 3965 397 4.49 0.28 401 5.69 1.31 394 4.85 0.41 397 4.09 0.16Sb 3695 377 4.68 2.06 381 6.08 3.12 374 5.27 1.36 376 4.36 1.94Cs 3615 359 4.59 0.65 362 6.00 0.39 357 7.22 1.23 358 4.36 0.77Ba 4359 442 2.90 1.68 447 6.83 2.78 440 6.43 1.05 442 2.58 1.56La 4575 465 3.91 1.65 470 7.70 2.76 462 7.70 1.04 464 3.75 1.54Ce 4485 453 4.30 1.16 458 6.38 2.22 450 6.34 0.50 453 3.89 1.04Pr 4305 438 3.76 1.79 442 6.94 2.89 435 6.92 1.17 437 3.55 1.68Nd 4315 438 3.57 1.60 443 7.50 2.72 435 7.13 0.99 437 3.47 1.49Sm 4515 459 3.95 1.76 464 7.12 2.85 456 6.50 1.11 458 3.65 1.65Eu 4615 466 3.92 1.06 471 7.57 2.16 463 7.17 0.43 465 3.69 0.95Gd 4449 449 3.56 1.10 454 7.77 2.22 446 7.02 0.48 448 3.45 0.99Tb 4435 447 3.58 0.98 452 7.42 2.08 445 6.88 0.35 447 3.40 0.87Dy 4275 431 3.31 0.95 436 7.87 2.09 428 6.89 0.34 431 3.30 0.85Ho 4495 453 3.49 0.95 458 7.84 2.07 450 6.91 0.32 453 3.35 0.84Er 4265 430 3.68 0.86 434 7.72 1.99 427 6.83 0.24 429 3.63 0.76Tm 4205 423 3.17 0.79 428 7.38 1.91 421 6.62 0.17 423 3.08 0.68Yb 4459 447 3.59 0.50 452 7.88 1.62 444 7.01 0.12 447 3.50 0.39Lu 4355 439 3.45 0.86 444 8.05 2.00 436 7.50 0.26 438 3.46 0.75Hf 4329 438 3.43 1.28 442 8.05 2.42 435 7.57 0.68 437 3.46 1.17Ta 4529 459 3.85 1.55 464 8.94 2.71 456 8.33 0.96 459 3.96 1.44W 4455 447 5.48 0.39 452 9.18 1.52 444 7.41 0.25 446 5.46 0.28Re 479 48 0.57 1.23 48 0.96 2.36 47 0.76 0.57 48 0.56 1.12Pt 3.28 3.3 0.05 2.83 3.3 0.09 4.11 3.3 0.08 2.30 3.3 0.05 2.73Au 235 24 0.26 2.28 24 0.46 3.44 23 0.35 1.62 23 0.25 2.17Tl 615 63 1.04 2.55 63 1.08 3.56 62 1.04 1.82 62 0.98 2.42Pb 4266 431 5.07 1.22 436 7.28 2.30 428 7.10 0.58 431 4.74 1.11Bi 3585 368 4.80 2.80 372 6.51 3.90 366 6.91 2.18 368 4.55 2.68Th 457.26 467.7 4.57 2.30 472.8 8.03 3.42 464.8 7.69 1.67 467.2 4.34 2.19U 461.56 459.6 5.88 0.41 464.5 7.95 0.65 456.7 7.66 1.05 459.1 5.55 0.52

a Bold italics indicates method with lowest difference relative to certified, reference or information (CRI) value. Superscript indicates published source ofCRI value.

This journal is ª The Royal Society of Chemistry 2008 J. Anal. At. Spectrom., 2008, 23, 1529–1537 | 1533

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Table 6 Calculated concentrations–NIST 612 & 614a

Element

NIST 612 NIST 614

CRI Range Most accurate CRI Range Most accurate

Li 425 42 to 48 42Si 1.69 1.8 to 2.1 1.8SiBe 385 38 to 43 38Si 0.679 <DL —B 355 54 to 63 54Si 1.49 19.7 to 23.4 19.7SiNa 104 0005 98 400 to 113 000 101 000Si 104 0009 103 000 to 122 000 103 000SiMg 775 60 to 68 68Ca 359 34 to 37 35OS

Al 11 2005 10 700 to 12 300 10 900OS 10 6009 10 400 to 12 300 10 600OS

Si 336 0005 343 000 to 387 000 343 000OS 337 0009 343 000 to 400 000 343 000OS

P 519 36 to 41 41Ca 139 11 to 13 13CaK 66.35 ND — 306 <DL —Ca 85 3005 74 100 to 75 700 75 700OS 85 7609 59 700 to 73 300 73 300OS

Sc 415 35 to 40 40Ca 1.69 <DL —Ti 449 37 to 42 42Ca 3.49 <DL —V 395 35 to 41 41Ca 19 1.0 to 1.1 1.0OS

Cr 369 34 to 39 34OS 1.89 <DL —Mn 385 35 to 41 36OS 1.49 1.3 to 1.5 1.3OS

Fe 516 ND — 199 <DL —Co 355 33 to 38 34OS 0.859 <DL to 0.88 0.88CaNi 38.86 39 to 45 39.1Si 19 <DL —Cu 375 36 to 42 37OS 1.376 <DL —Zn 385 40 to 46 40Si 2.59 <DL —Ga 365 35 to 40 36OS 1.59 1.2 to 1.4 1.4CaGe 355 36 to 42 36Si 0.899 1.11 to 1.29 1.11SiAs 375 27 to 31 31Ca 0.669 <DL —Se — 15 to 17 — — 0.5 to 0.8 —Rb 31.46 28.6 to 33.0 32.9Ca 0.8556 1.157 to 1.171 1.157CaSr 78.46 72.8 to 83.8 74.4OS 45.86 41.9 to 49.6 42.6OS

Y 385 33 to 38 38Ca 0.89 0.6 to 0.7 0.7CaZr 389 34 to 39 39Ca 0.849 0.85 to 1.00 0.85SiNb 409 33 to 38 38Ca 0.819 0.68 to 0.80 0.80CaMo 385 35 to 40 40Ca 0.89 0.8 to 0.9 0.8SiRh 0.98 0.9 to 1.0 0.9Si 1.68 1.6 to 1.9 1.6SiPd 1.18 1.1 to 1.3 1.1Si 28 2 to 3 2SiAg 226 18 to 21 21Ca 0.426 0.43 to 0.51 0.43SiCd 28.35 24.1 to 27.7 27.7Ca 0.589 <DL —In 435 33 to 38 38Ca 0.889 0.70 to 0.82 0.82CaSn 385 35 to 40 40Ca 1.69 <DL —Sb 385 30 to 34 34Ca 0.789 0.70 to 0.82 0.82CaCs 425 36 to 42 42Ca 0.669 0.61 to 0.84 0.62OS

Ba 39.710 35.1 to 40.4 40.4Ca 3.29 3.0 to 3.5 3.0OS

La 35.810 34.2 to 39.3 34.9OS 0.729 0.66 to 0.78 0.67OS

Ce 38.710 35.4 to 40.7 40.7Ca 0.819 0.72 to 0.85 0.85CaPr 37.25 33.6 to 38.7 38.7Ca 0.769 0.68 to 0.80 0.80CaNd 35.910 32.6 to 37.5 37.5Ca 0.749 0.73 to 0.85 0.74OS

Sm 38.110 34.2 to 39.3 39.3Ca 0.759 0.71 to 0.85 0.73OS

Eu 3510 34 to 39 34OS 0.769 0.72 to 0.85 0.73OS

Gd 36.710 33.2 to 38.1 38.1Ca 0.759 0.78 to 0.87 0.78SiTb 365 33 to 38 38Ca 0.739 0.63 to 0.74 0.74CaDy 3610 31 to 36 35Ca 0.749 0.62 to 0.74 0.74CaHo 385 33 to 38 38Ca 0.749 0.64 to 0.76 0.76CaEr 3810 31 to 36 36Ca 0.749 0.57 to 0.68 0.68CaTm 385 31 to 35 35Ca 0.739 0.58 to 0.68 0.68CaYb 39.210 33.4 to 38.4 38.4Ca 0.779 0.63 to 0.74 0.74CaLu 36.910 31.6 to 36.3 36.3Ca 0.739 0.59 to 0.70 0.70CaHf 355 33 to 37 33OS 0.79 0.6 to 0.7 0.7CaTa 405 34 to 39 39Ca 0.799 0.68 to 0.81 0.81CaW 405 37 to 42 38OS 0.889 0.78 to 0.92 0.92CaRe 6.68 6.1 to 7.0 6.3OS 0.178 0.16 to 0.19 0.17OS

Pt 2.68 2.5 to 2.9 2.5OS 2.38 2.4 to 2.9 2.43SiAu 5.15 4.5 to 5.1 5.1Ca 0.459 0.50 to 0.59 0.50SiTl 15.15 14.2 to 16.4 14.5OS 0.289 0.27 to 0.32 0.28OS

Pb 38.576 34.98 to 40.30 40.30Ca 2.326 2.63 to 3.11 2.63SiBi 305 29 to 33 30OS 0.589 0.59 to 0.70 0.59SiTh 796 34 to 39 39Ca 0.7486 0.668 to 0.790 0.79CaU 386 33 to 38 38Ca 0.8236 0.782 to 0.924 0.79OS

a — calculation not possible due to lack of CRI value or measured concentration less than DL. Superscript indicates published source of CRI value.Subscript indicates standardization method yielding most accurate result.

1534 | J. Anal. At. Spectrom., 2008, 23, 1529–1537 This journal is ª The Royal Society of Chemistry 2008

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Table 7 Calculated concentrations–BCR-2G, BHVO-2 & BIRa

Element

BCR-2G BHVO-2 BIR-1

CRI RangeMostaccurate CRI Range

Mostaccurate CRI Range

Mostaccurate

Li9 99 9–12 9Si 4.813 4.1–4.8 4.8Ca 3.29 2.5–3.6 2.8FeBe 2.39 2.3–2.7 2.3Si 114 <DL — 0.1220 <DL —B 611 15.3–19.7 15.3Si — 13.7–15.9 — 0.3321 12.40–17.87 12.4SiNa 24 0009 17 800–23 000 23 000Ca 16 50015 12 000–13 900 13 900Ca 13 4009 9590–14 000 14 000CaMg 22 4009 19 600–25 200 20 400OS 43 60015 48 100–56 000 48 100Fe 58 0009 56 600–82 400 56 600SiAl 70 9009 72 900–93 600 72 900Si 71 40015 74 300–86 400 74 300Fe 81 5009 76 500–111 000 82 300OS

Si 254 0009 254 000–327 000 264 000Fe 233 00015 231 000–269 000 231 000Fe 223 0009 241 000–326 000 241 000OS

P 16209 1180–1520 1530Ca 120015 839–980 980Ca 1209 79–115 115CaK 14 40010 15 600–20 100 15 600Si 430015 4430–5160 4430Fe 23022 150–220 220CaCa 50 5009 39 400–41 100 41 100OS 81 50015 70 200–71 700 71 700OS 95 8009 66 200–73 800 73 800FeSc 339 28–36 36Ca 3215 27–32 32Ca 439 32–46 46CaTi 14 1009 11 700–15 000 15 000Ca 16 30015 14 200–16 600 16 600Ca 56009 4380–6350 4880FeV 4259 353–454 454Ca 31715 263–307 307Ca 3199 238–346 346CaCr 179 13–17 17Ca 28015 250–292 292Ca 3919 305–444 444CaMn 15509 1430–1840 1490OS 13209 1340–1560 1340Fe 13609 1240–1800 1380FeFe 96 4009 93 000–119 000 97 000OS 88 60014 89 700–103 000 89 700Si 82 4009 73 900–107 000 79 600OS

Co 389 34–44 35OS 4515 41–47 47Ca 529 47–68 52FeNi 139 <DL–14 14Ca 11915 110–128 113OS 1669 157–229 170OS

Cu 219 <DL–26 26Ca 12715 104–121 121Ca 1199 98–143 110FeZn 1259 149–193 149Si 10315 94–110 96OS 729 90–132 90SiGa 239 30–38 30Si 229 20–23 23Ca 15.39 15.2–22.2 15SiGe 1.510 <DL — 1.69 <DL — 1.49 <DL —As — <DL–2.5 2.5Ca — <DL — 0.4421 <DL 2.22CaSe — <DL — — <DL — 0.02423 <DL —Rb 4710 40–51 51Ca 9.119 7.51–8.74 8.74Ca 0.29 <DL —Sr 34210 290–373 373Ca 3969 353–410 410Ca 10924 87.1–126.4 97FeY 359 26–34 34Ca 2615 19–22 22Ca 15.69 10.2–14.7 14.7CaZr 1849 149–191 191Ca 17215 134–156 156Ca 149 10.7–15.5 12FeNb 12.59 10.0–12.9 13Ca 18.19 14.1–16.4 16.4Ca 0.559 0.38–0.55 0.55CaMo 2709 229–295 295Ca 49 3.4–4.0 4Ca 0.0725 <DL —Rh — <DL — 0.00716 <DL — 0.0003426 <DL —Pd — <DL — 0.002916 <DL — 0.006116 <DL —Ag 0.53 0.6–0.7 0.6Si — 0.35–0.40 — 0.03626 <DL —Cd 0.29 <DL — 0.0617 <DL — 0.09727 <DL —In 0.119 0.13–0.17 0.13Si — 0.08–0.09 — 0.05528 <DL —Sn 2.69 2.5–3.1 2.6OS 1.717 1.8–2.1 1.8Fe 0.622 <DL —Sb 0.359 0.31–0.38 0.32OS 0.139 0.10–0.12 0.12Ca 0.469 0.47–0.69 0.47SiCs 1.169 0.91–1.30 1.08OS 0.19 <DL — 0.0079 <DL —Ba 68310 580–745 745Ca 13118 118–137 137Ca 7.1422 5.7–8.3 6.32FeLa 24.710 21.9–28.1 22.8OS 15.218 13.2–15.4 15.4Ca 0.6159 0.50–0.70 0.539FeCe 53.310 42.8–55.0 55.0Ca 37.518 31.8–37.0 37.0Ca 1.929 1.5–2.2 2.15CaPr 6.79 5.4–6.9 6.9Ca 5.359 4.22–4.90 4.90Ca 0.379 0.30–0.43 0.33FeNd 28.910 24.0–30.8 30.8Ca 24.518 20.8–24.2 24.2Ca 2.389 1.9–2.7 2.10FeSm 6.5910 5.64–7.25 7.25Ca 6.0718 5.11–5.93 5.93Ca 1.129 0.8–1.2 1.22CaEu 1.9710 1.87–2.40 1.95OS 2.0718 1.86–2.13 2.13Ca 0.5322 0.43–0.62 0.48FeGd 6.7110 5.43–6.97 6.97Ca 6.2418 4.85–5.62 5.62Ca 1.879 1.4–2.0 1.97CaTb 1.029 1.01–1.31 1.01Si 0.929 0.72–0.82 0.82Ca 0.369 0.26–0.37 0.37CaDy 6.4410 5.08–6.52 6.52Ca 5.3118 3.96–4.59 4.59Ca 2.5122 1.8–2.6 2.57CaHo 1.279 1.18–1.52 1.23OS 0.989 0.79–0.86 0.86Ca 0.5622 0.39–0.55 0.55CaEr 3.710 2.8–3.5 3.5Ca 2.5418 1.85–2.12 2.12Ca 1.669 1.1–1.6 1.64CaTm 0.519 0.42–0.74 0.44OS 0.339 0.26–0.29 0.29Ca 0.259 0.18–0.25 0.25CaYb 3.3910 2.74–3.53 3.53Ca 218 1.6–1.8 1.8Ca 1.6522 1.2–1.8 1.75CaLu 0.50310 0.445–0.754 0.464OS 0.27418 0.220–0.250 0.250Ca 0.259 0.18–0.24 0.24CaHf 4.849 4.03–5.17 5.17Ca 4.369 3.44–3.98 3.98Ca 0.5829 0.42–0.61 0.605CaTa 0.789 0.75–1.08 0.75Si 1.149 0.93–1.06 1.06Ca 0.03579 <DL —W 0.59 <DL — 0.219 0.21–0.24 0.21Si 0.0726 <DL —Re 0.006212 <DL — 0.0005416 <DL — 0.0006316 <DL —Pt 0.7812 0.31–0.40 0.40Ca 0.0116 <DL — 0.004316 <DL —Au — <DL–0.03 — — 0.27–0.31 — 0.001829 <DL —Tl 0.39 0.25–0.32 0.3Ca — 0.03 — 0.0059 <DL —Pb 119 10–12 10OS 1.69 1.5–1.7 1.7Ca 3.19 4.3–6.2 4.25SiBi 0.059 <DL — — <DL — 0.00430 <DL —Th 5.99 5.1–6.5 6.5Ca 1.229 1.02–1.16 1.16Ca 0.0329 <DL —U 1.699 1.54–1.98 1.61OS 0.40319 0.34–0.39 0.393Ca 0.019 <DL —

a — calculation not possible due to lack of CRI value or measured concentration less than DL. Superscript indicates standardization method yieldingmost accurate result.

This journal is ª The Royal Society of Chemistry 2008 J. Anal. At. Spectrom., 2008, 23, 1529–1537 | 1535

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Table 8 Certified reference materials tentative valuesa

CRM Element ¼ tentative valuestandardization method used

NIST 612 Se ¼ 15.08 ppmSi

NIST 614 Se ¼ 0.48 ppmSi

BCR-2G As ¼ 2.5 ppmCa, Au ¼ 0.03 ppmCa

BHVO-2 Ag ¼ 0.40 ppmCa, In ¼ 0.09 ppmCa, Au ¼ 0.31 ppmCa,Tl ¼ 0.03 ppmOS, Bi ¼ 0.02 ppmOS

a Superscript indicates standardization method most likely to yield mostaccurate result.

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standard resulted in the most accurate results for the greatest

number (21) of elements (P, Co, Ga, Rb, Y, Nb, In, Sb, Ce, Pr,

Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, and Th). Scaling the

oxide concentrations resulted in the most accurate results for

16 elements (Mg, Al, Si, Ca, V, Mn, Sr, Cs, Ba, La, Nd, Sm, Eu,

Re, Tl and U). Using Si as an internal standard resulted in the

most accurate results for 14 elements (Li, B, Na, Ge, Zr, Mo, Rh,

Pd, Ag, Gd, Pt, Au, Pb and Bi).

Average analytical errors were less than approximately �20%

for the majority of elements included in the analysis of BCR-2G.

Eight elements (B, Cu, Zn, Ga, Ag, In, Tm, and Pt) had average

analytical errors greater than approximately �20%. Using Ca as

an internal standard resulted in the most accurate results for the

greatest number (28) of elements (Na, P, Sc, Ti, V, Cr, Ni, Cu,

As, Rb, Sr, Y, Zr, Nb, Mo, Ba, Ce, Pr, Nd, Sm, Gd, Dy, Er, Yb,

Hf, Pt, Tl, and Th). Scaling the oxide concentrations resulted in

the most accurate results for 15 elements (Mg, Ca, Mn, Fe, Co,

Sn, Sb, Cs, La, Eu, Ho, Tm, Lu, Pb, and U). Using Si and Fe

as internal standards resulted in the most accurate results for

11 elements (Li, Be, B, Al, K, Zn, Ga, Ag, In, Tb, and Ta) and

1 element (Si), respectively.

Average analytical errors were less than approximately �20%

for the majority of elements included in the analysis of BHVO-2.

Five elements (Na, P, Y, Dy and Er) had average analytical

errors greater than approximately�20%. Using Ca as an internal

standard resulted in the most accurate results for the greatest

number (37) of elements (Li, Na, P, Sc, Ti, V, Cr, Co, Cu, Ga,

Rb, Sr, Y, Zr, Nb, Mo, Sb, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb,

Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, Pb, Th and U). Using Fe as

an internal standard resulted in the most accurate results for

6 elements (Mg, Al, Si, K, Mn and Sn). Scaling the oxide

concentrations resulted in the most accurate results for

3 elements (Ca, Ni, and Zn) and using Si as an internal standard

resulted in the most accurate results for 2 elements (Fe, and W).

Average analytical errors were less than approximately �20%

for the majority of elements included in the analysis of BIR-1.

Eight elements (B, P, K, Zn, Y, Ho, Er and Pb) had average

analytical errors greater than approximately �20%. Using Ca as

an internal standard resulted in the most accurate results for the

greatest number (20) of elements (Na, P, K, Sc, V, Cr, As, Y, Nb,

Ce, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Hf). Using Fe as

an internal standard resulted in the most accurate results for

13 elements (Li, Ca, Ti, Mn, Co, Cu, Sr, Zr, Ba, La, Pr, Nd, and

Eu). Using Si as an internal standard resulted in the most accu-

rate results for 6 elements (B, Mg, Zn, Ga, Sb, and Pb). Scaling

the oxide concentrations resulted in the most accurate results

for 4 elements (Al, Si, Fe, and Ni).

Average analytical errors for all elements determined were

lowest for NIST 610 (typically less than �2%), which is not

surprising considering NIST 610 was used as the external

calibration standard (i.e., 100% matrix-matched). Despite the

similarity in the bulk composition of the CRMs (i.e., all are sili-

cate glasses), analytical errors varied depending on the reference

material analyzed. NIST 612 and 614 had the next lowest average

analytical errors for all elements determined (typically less than

�10%) and the USGS CRMs (BCR-2G, BHVO-2 and BIR-1)

had the highest average analytical errors for all elements

determined (typically less than � 20%). Possible sources of the

observed analytical error (i.e., deviation of measured values from

1536 | J. Anal. At. Spectrom., 2008, 23, 1529–1537

CRI values) aremanifold and include elemental fractionation,31,32

CRM contamination,33,34 and, possibly, inaccurate CRI values.

The majority of the elements displaying relatively high

analytical errors have high (>1.2) or low (<0.8) fractionation

factors31,32 (Li, B, Na, P, Sc, Ti, Cu, Zn, Ga, Ge, As, Rb, Nb, Ag,

Cd, In, Sn, Sb, Au, Tl, Pb, and Bi). The relatively high analytical

errors observed for these could be the result of ablation-related

elemental fractionation.

Contamination of natural and synthetic samples, particularly

by elements such as B, is well documented.33,34 The highest

analytical errors observed in this study were those obtained for B

(e.g., NIST 614 and BIR-1), which was consistently measured at

concentrations in excess of the CRI values in the CRMs.

Contamination of the CRMs is the most likely explanation

for the relatively high analytical errors observed for B.

For the purpose of this investigation, it has been assumed that

the published CRI values are accurate. Evaluation of the relative

accuracy of the CRI values is outside the scope of this investi-

gation.

Use of an internal standard element (Si, Ca or Fe) or oxide

scaling typically yielded excellent (less than �2%) to acceptable

(less than �20%) average analytical errors for all of the CRMs

considered in this study. Quantification of element concentra-

tions from LA-ICPMS analysis using oxide scaling was as

accurate and precise as using an internal standard for a range

of silicate compositions and enabled the determination of

element concentrations without the concentration of one or

more elements being known beforehand.

Although this paper presents results only for silicate glass

CRMs, this method has been applied to chemically complex,

silicate minerals (amphibole and pyroxene) from the Strange

Lake peralkaline complex, Quebec/Labrador.35,36 Results

obtained by LA-ICPMS analysis using oxide scaling yielded

comparable accuracy and precision to those obtained for the

silicate glass CRMs and were similar to those obtained using an

EMP. Oxide scaling alone yielded mineral formulae that were

as accurate as those obtained using internal standards.

Tentative concentrations for elements without CRIvalues

In addition to providing a measure of analytical accuracy for

elements with certified, reference or information values, data

obtained during this study were used to calculate tentative

concentrations for elements that currently do not have published

certified, reference, or information values (Table 8). For NIST

612 and 614, tentative values were obtained for Se using Si as an

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internal standard. For BCR-2G, tentative values were obtained

for As and Au using Ca as an internal standard. For BHVO-2,

tentative values were obtained for Ag, In, Au, Tl and Bi using

either Ca as an internal standard (Ag, In, and Au) or by oxide

scaling (Tl and Bi).

Conclusions

Based on laboratory analyses, and interpretations of data

resulting from these analyses, the following conclusions can be

drawn:

� Quantitative analysis of synthetic silicate certified reference

materials by LA-ICPMS without using a previously-determined

or estimated internal standard element and without using alter-

native calibration (e.g., liquid introduction) strategies is possible

by conducting comprehensive elemental analyses and performing

oxide scaling. Element concentrations calculated using oxide

scaling typically have comparable or better average analytical

errors (typically less than �2% to �20%) than those obtained

using common internal standard elements (e.g., Si, Ca or Fe).

� Element concentrations determined for the six CRMs using

oxide scaling had similar accuracy and precision to those

obtained for NIST 612, NIST 614, BCR-2G, BHVO-2, and BIR-

1 using NIST 610 as an external calibration standard and Si, Ca,

and Fe as internal standards. Oxide scaling provides data of

sufficient accuracy and precision for use in determining the

chemical formulae for unknown minerals analyzed using

LA-ICPMS.

Acknowledgements

The authors thank two anonymous reviewers for providing input

on earlier versions of this manuscript. The Natural Sciences and

Engineering Research Council of Canada (NSERC) provided

funding to support this research.

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