04 Matrix Modifiers for Graphite Furnace Analysis

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Shimadzu (Asia Pacific) Pte L

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MATRIX MODIFIER (MM) FOR GRAPHITE FURNACE ANALYSIS (GFA)

This article is a guide regarding the use of MM in GFA. Although it is derived from

several sources, it is not comprehensive and final. As could be seen, more than one type of MM can be used for each element. End-users are encouraged to try out the various types of MM, the appropriate MM concentration as well as the furnace temperature program to suit the various sample matrixes.

ELEMENT/SAMPLE/MM REMARKS Aluminium (Al)

La(NO3)3 Effective with alloying. *City H2O

10 ppm Mg(NO3)2 or 10 ppm NH4Cl; sample : modifier = 1:1

Serum and blood Dilute Triton X-100

Antimony (Sb) Cu best, Ni, Pt also effective Alloying. La(NO3)3 Alloying.

*City H2O 10 ppm Pd using Pd(NO3)2 or 10 ppm Ni using Ni(NO3)2; sample : modifier = 1:1

@Electrolytic copper ore 200 ppb La from La(NO3)3

50-1000 ppm Ni(NO3)2 Permits a higher ashing temperature, stabilises and enhances the signal.

100 ppm Pd(NO3)2 with 2.5% ascorbic acid

500-2000 ppm Pd solution + reducing agent such as ascorbic acid

Permits a higher ashing temperature and enhances the analyte signal.

Use secondary wavelength or Zeeman background correction if interference is expected from high Pb concentration which may cause a measurable spectral interference at 217.6 nm.

Arsenic (As) Pd best, Mo, Zr, Ba also good Coexistence with Ni is effective. La(NO3)3 Production of As2O6 seems to be effective. Mg(NO3)2, Ni(NO3)2 Increase ashing temperature. (PTO)

SAP/CSC/CAM/AAS-007aFeb 2002 td, Singapore

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Shimadzu (Asia Pacific) Pte Ltd, Singapore

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ELEMENT/SAMPLE/MM REMARKS Arsenic (As) (cont)

*City H2O 10 ppm Pd using Pd(NO3)2 or 10 ppm Ni using Ni(NO3)2; sample : modifier = 1:1

@Electrolytic copper ore 200 ppb La from La (NO3)3

$10 ppm Ni from Ni(NO3)2 $Formation of nickel arsenide which is stable up to 900oC so that higher ashing temperature can be used.

100-2000 ppm Pd or 10 l of 500 ppm Pd or 100-2000 ppm Pt or 50 ppm Ni or 500-2000 ppm Pd solution + reducing agent such as ascorbic acid

Permits higher ashing temperature and enhances signal.

Samples may be subjected to losses of As during sample preparation as elemental As and many of its compounds are volatile. Process spiked samples and relevant standard reference materials to determine if the chosen dissolution method is appropriate.

Employ with caution the selection temperatures and times of drying and ashing cycles.

Nickel nitrate To minimise volatilisation losses during drying and ashing.

Employ simultaneous background correction to avoid erroneously high results due to severe non-specific absorption and light scattering caused by matrix components during atomisation. As analysis is particularly susceptible to these problems because of its low analytical wavelength (193.7 nm).

Use Zeeman background correction or any appropriate background correction technique to overcome severe positive interference caused by Al, especially when using D2 arc background correction.

Clean tube by operating the furnace at full power at regular intervals to remove memory effect caused by analyte that is not completely volatilised and removed from furnace during atomisation.

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ELEMENT/SAMPLE/MM REMARKS Barium (Ba)

La(NO3)3 Effective with alloying. Formation of less volatile barium carbide can

cause losses of sensitivity and memory effects. Optimise furnace parameters to minimise

severe physical and chemical interferences caused by long residence time and high concentration of the analyte in optical path of graphite furnace.

Do not use N2 as purge gas because of possible chemical interference.

Do not use halide acids. Beryllium (Be)

La(NO3)3 Effective with alloying. Optimise furnace parameters to minimise

severe physical and chemical interferences caused by long residence time and high concentration of the atomised sample in optical path of graphite furnace.

Require simultaneous background correction to avoid erroneously high results due to severe non-specific absorption and light scattering caused by matrix components during atomisation.

Bismuth (Bi) Pb MIBK extract.


1000 ppm Ni or 1000 ppm Pd Permits a higher ashing temperature and enhances signal.

Boron (B) $500 ppm Ca $May enhance sensitivity. 100 ppm Ba(OH)2 or 100 or 1000 ppm La(NO3)3/LaCl3

Enhances signal.

Cadmium (Cd) Blood, serum, urine

Pd(NO3)2 + NH4NO3 ; (NH4)2HPO4 + HNO3

ppb level

La(NO3)3 Effective with alloying. Mg(NO3)2 ; (NH4)H2PO4 + HNO3 or Mg(NO3)2

Addition of F, SO42-, PO43- effective.

1% (NH4)2HPO4 Ashing temperature can be increased. (PTO)

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ELEMENT/SAMPLE/MM REMARKS Cadmium (Cd) (cont)

*City H2O 10 ppm Pd using Pd(NO3)2 or 10 ppm NH4NO3; sample : modifier = 1:1

*Environmental H2O; Wastewater #Vegetables, fruits, grains, beans, potatoes, meat, fish, fats, oils, dairy products, spirits, alcoholic beverages, processed food

*10 ppm Pd using Pd(NO3)2; sample : modifier = 1:1

$1% (w/v) (NH4)2HPO4 or 1% (w/v) (NH4)SO4 or 0.1% (w/v) (NH4)MoO4.4H2O or 1% (v/v) H2SO4 or H3PO4 can be substituted for ammonium salt solutions.

$By the addition of phosphate ions, ashing temperature can be increased due to the formation of cadmium phosphate which is stable up to 650-800oC.

Excess NaCl 2% NH4NO3 or 2% NH4 oxalate

To aid in low temperature removal of NaCl through formation of NH4Cl and NaNO3 (reduction in non-atomic absorption).

Seawater 2% (NH4)H2PO4 or 2% NH4 oxalate

Soil 3% H3PO4 or 1-2% (NH4)H2PO4 ; 40 l modifier added to 20 l sample.

Plant tissue 2% H3PO4 or 2% (NH4)H2PO4 ; 40 l modifier added to 20 l sample.

Whole Blood 2% (NH4)2H2PO4

Infant formula, skim milk powder; Streams, Effluents

0.5% (w/v) (NH4)H2PO4

1000 ppm H3PO4 or 1000 or 5000 ppm (NH4)H2PO4

Conversion to less volatile phosphate so that higher atomisation temperature can be used and ensures a smooth peak.


Permits a higher ashing temperature.

Require simultaneous background correction to avoid erroneously high results due to severe non-specific absorption and light scattering caused by matrix components during atomisation. (PTO)

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ELEMENT/SAMPLE/MM REMARKS Cadmium (Cd) (cont)

Ammonium phosphate or other modifiers

To minimise loss due to excess chloride which may cause premature volatilisation of Cd.

Use Cd-free pipette tips. Cesium (Cs)

$0.2% (v/v) H2SO4 Chromium (Cr)

La(NO3)3 Effective with alloying. *City H2O; Environmental H2O; Wastewater

10 ppm NH4Cl; sample : modifier = 1:1

Seawater 1% Mg(NO3)2 or 1% HNO3

Reduces background signal, minimises interferences.

Seawater 2-10% NH4NO3 or 2% NH4 oxalate




Calcium nitrate Low concentrations of Ca and/or phosphate may cause interferences. At above 200 mg/L, Cas effect is constant and eliminates the effect of phosphate.

Do not use N2 as purge gas because of a possible CN band interference.

May require background correction because non-specific absorption and scattering can be significant at analytical wavelength.

Cobalt (Co) 0.5% Fe(NO3)2 To prevent coexistence of halogenide. Seawater

2-10% NH4NO3 or 2% NH4 oxalate



Verify that interference caused by excess chloride is absent by standard additions.

Copper (Cu) La(NO3)3 Effective with alloying. Soil with excess NaCl

40 l of 1% NH4NO3 added to 20 l of sample.

(PTO)

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ELEMENT/SAMPLE/MM REMARKS Copper (Cu) (cont) Water and seawater

3000 ppm Na2O2 Substantially reduces interferences caused by NaClO4; alkali metal halides; Al and Mg halides.




500-2000 ppm Pd solution + reducing agent e.g. ascorbic acid


May require background correction for non-specific absorption and scattering which can be significant at analytical wavelength.

Gallium (Ga) Ni

Ni checks GaO production and avoids inorganic matter interference.

500 ppm Pd or 5 l 100 ppm Pd or 1000 ppm Ni(NO3)2

Permits higher ashing temperature, enhances signal and increases sensitivity.

Germanium (Ge) 500 ppm Pd or 5 l of 100 ppm Pd Permits a higher ashing temperature,

enhances signal and improves sensitivity. Gold (Au) 0.25% Ni(NO3)2 Permits a higher ashing temperature. 500-2000 ppm Pd solution + reducing agent such as Acorbic acid


Indium (In) Pd Pd checks production of InO sublimation. La(NO3)3 Alloying. $1% (w/v) ammonium fluoride, NH4F $Higher ashing temperature can be used. 1000 ppm Pd or 5 l of 1000 ppm Pd A higher ashing temperature can be used and

improves sensitivity. Iron (Fe) Seawater

2-10% NH4NO3 or 2% NH4 oxalate



As Fe is a universal contaminant, great care should be taken particularly at low levels.

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ELEMENT/SAMPLE/MM REMARKS Lead (Pb)

Mg(NO3)2 Coexistence with NaCl, KCl, MgCl, etc prevents PbCl2 sublimation.

La(NO3)3 ; Pd, Pt (g level) Effective by addition of HNO3, high sensitivity obtained by alloying.

*City H2O 10 ppm Pd from Pd(NO3)2 or 10 ppm NH4Cl; sample : modifier = 1:1

*Environmental H2O; Wastewater #Vegetables, fruits, grains, beans, potatoes, meat, fish, fats, oil, dairy products, spirits, alcoholic beverages, processed foods

*10 ppm Pd from Pd(NO3)2; sample: modifier = 1:1


Medicines

10 ppm Pd from Pd(NO3)2



Seawater 10% ascorbic acid

Suppresses matrix interferences.


Blood 0.1% Triton X-100

Dispersing agent -facilitates dispersing.

Infant formula, skim milk powder; Streams, Effluents

0.5% (w/v) (NH4)H2PO4

1000 or 5000 ppm H3PO4 or 5000 ppm (NH4)H2PO4

Permits a higher ashing temperature and stabilises the signal.

0.5-1% (v/v) EDTA or 0.5-1% (v/v) citrate or 0.5-1% (v/v) oxalate

Stabilises Pb which atomises at a lower temperature than does a nitrate or chloride matrix.



Require background correction. Phosphoric acid May be necessary if poor recoveries are

obtained.

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ELEMENT/SAMPLE/MM REMARKS Manganese (Mn)

La(NO3)3 Effective with alloying. HNO3 Ashing temperature can be increased from

1100 to 1150oC. *City H2O; Waste H2O



Suppresses matrix interferences.





Must use background correction. Mercury (Hg)

Soil Organic acid (succinic acid, tartaric acid)

Sulfide + HNO3 Volatization prevention as HgS. HCl + H2O2 K2Cr2O7 + Na2S

For prevention of reduction in vaporisation as HgS.

Au, Pt, Pd (g level) Se

To prevent volatization by amalgamation.

$Ammonium Sulfide $Volatization prevention as HgS which is stable at 150oC to prevent loss of mercury vapour during drying cycle.

$For diluent, use: 1) 1000 ppm Te in 1% HCl or 2) 0.1% K2Cr2O7 in 0.5% HNO3

$Organo-sulfur compounds such as cysteine.

$As complexing agents to increase ashing temperature to 500oC to minimise chemical and bulk matrix interference.

Excess (NH4)2S Stabilises the signal. 500-2000 ppm Pd solution + reducing agent such as ascorbic acid or 1000 ppm Pd

Permits a higher ashing temperature and enhances the signal.

Molybdenum (Mo) *City H2O

10 ppm asorbic acid; sample : modifier = 1:1


Suppresses matrix interferences. (PTO)

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ELEMENT/SAMPLE/MM REMARKS Molybdenum (Mo) (cont)

Use pyrolytically coated graphite tube as Mo is prone to carbide formation.

May require cleaning of furnace after analysis of more concentrated samples or standards as memory effects are possible.

Nickel (Ni) *City H2O


Seawater 1% Mg(NO3)2 or 1% HNO3

Reduces background signal, minimises interferences.




Background correction is strongly recommended as Ni can suffer from severe non-specific absorption and scattering caused by matrix components during atomisation.

The use of separate graphite furnace tubes and contact rings from those used in analysis of As and Se where nickel nitrate MM is used is strongly recommended to minimise severe memory effects.

Phosphorus (P) La(NO3)3 e.g. $0.1% La from La(NO3)3 or 0.2% from nitrate

Sensitivity improves 6 times. Permits a higher ashing temperature and improves precision.

$200 ppm Ni from Ni(NO3)2 or 2000 ppm Ni from Ni(NO3)2

$Higher ashing temperature can be used. Improves precision.

5 l of 1000 ppm La Selenium (Se)

Mg(NO3)2 Coexistence with Ni is effective (NiSe produced).

Al, Cu, Ni, Pd, Pt Pd particularly good, PdSe produced. Cu, Mo and Ni Ashing temperature can be increased from

1000 -1100oC. *City H2O

10 ppm Pd; sample : modifier = 1:1

$10 ppm from Ni(NO3)2 $Formation of nickel selenide which is stable up to 900 or 1000oC. (PTO)

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ELEMENT/SAMPLE/MM REMARKS Selenium (Se) (cont) Whole blood

Dilute blood 5 times in diluting agent consisting of: 0.5% Triton X-100 + 0.125% Dow Corning Antifoam B + 0.25% ascorbic acid. Add 0.05% Pd as MM.

1% Ni(NO3)2 or 10 l of 500 ppm Pd Permits a higher ashing temperature and enhances the signal.

Samples may be subjected to losses of Se during sample preparation as elemental Se and many of its compounds are volatile. Process spiked samples and relevant standard reference materials to determine if the chosen dissolution method is appropriate.

Employ with caution the selection of temperatures and times for drying and ashing cycles.

Nickel nitrate To minimise volatilisation losses during drying and ashing.

Requires simultaneous background correction to avoid erroneously high results due to severe non-specific absorption and light scattering caused by matrix components during atomisation because of its low analytical wavelength (196.0 nm).

Zeeman background correction is useful when high Fe levels can give overcorrections with D2 background.

Clean tube by operating furnace at full power at regular intervals to remove memory effect caused by analyte that is not completely volatilised and removed from furnace during atomisation.

1% Ni from nickel nitrate To lessen interferences caused by chlorides (> 800 mg/L) and sulfate (> 200 mg/L).

Silicon (Si) La(NO3)3 Effective with alloying. $2 ppm Ba and 100 ppm La, both from chloride salts

$Minimise silicon carbide formation and ashing temperature can be increased to 1000oC.

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ELEMENT/SAMPLE/MM REMARKS Silver (Ag) 1% (NH4)H2PO4 Permits a higher ashing temperature. 500-2000 ppm Pd + reducing agent such as ascorbic acid


Employ simultaneous background correction to avoid erroneously high results due to severe non-specific absorption and light scattering caused by matrix components during atomisation.

Should clean tube by operating furnace at higher atomisation temperature to remove memory effect caused by analyte that is not completely volatilised and removed from furnace during atomisation.

Store Ag standards in brown bottles as they are light sensitive and have the tendency to plate out on container walls.

Avoid HCl as silver chloride is insoluble unless the Ag is already in solution as a chloride complex.

Tellurium (Te) $10 ppm Ni from Ni(NO3)2 $To maximize ashing temperature. 0.1% or 1% Ni(NO3)2


5 l 1000 ppm Pd Permits a higher ashing temperature and enhances the signal.

Terbium (Tb) $0.02 mg Ni from Ni(NO3)2

Thallium (Tl) Pd + HClO4 Coexistence with ascorbic acid is effective, Pd

checks TlCl production. La(NO3)3 Alloying. 1% H2SO4 Stabilises the signal. 500-2000 ppm Pd + reducing agent such as ascorbic acid


Require background correction. HCl or excessive chloride will cause

volatilisation of Tl at low temperature. Verify that losses are not occurring by spiking samples or using standard additions method.

Pd A suitable MM.

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ELEMENT/SAMPLE/MM REMARKS Tin (Sn)

Mg(NO3)2, (NH4)2HPO4 Use with ascorbic acid to prevent interference. La(NO3)3 Effective by alloying. K2MO4 Sensitivity improves remarkably but chloride

interference exists. NH4NO3, (NH4)2C2O4 No chloride interference.

#Spirits, alcoholic beverage, processed foods

10 ppm Pd using Pd(NO3)2

$0.2% (w/v) K2Cr2O7 + 1% HCl or 3% HNO3 + 10% (1 : 1) NH4OH

0.1% diammonium hydrogen citrate Complexes with Sn and enhances sensitivity. Stabilises the Sn in solution and facilitates production of a single peak.



500 ppm Pd or 5 l of 100 ppm Pd Permits a higher ashing temperature and enhances the signal.

Vanadium (V) Seawater

10% ascorbic acid Suppresses matrix interferences.

Require background correction. Clean furnace before and after analysis as Va

is refractory and prone to form carbides. Do not use N2 as purge gas.

Yttrium (Y) $0.02 mg Ni from Ni(NO3)2

Zinc (Zn) Succinic acid, oxalic acid MaCl2 produces ZnCl2 and sublimation.

Organic acid checks it. Should use background correction. As Zn is a universal contaminant, great care

should be taken. Notes: The information is mainly taken from Shimadzu AAS Cookbook Section 2. The rest are taken from the following: = Shimadzu AAS Cookbook Section 4 (Measuring Conditions of Elements of

Furnace Analysis Method) * = Shimadzu AAS Cookbook Section 5 (Water Analysis and Air Analysis)

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Notes (cont): # = Shimadzu AAS Cookbook Section 6 (Foodstuffs Analysis, Fertilizer and Feed

Analysis) @

= Shimadzu AAS Cookbook Section 8 (Non-ferrous Metals Analysis) = Shimadzu AAS Cookbook Section 10 (Medicines and Biological Substances) $ = CRC Handbook Of Furnace AAS = Analytical Methods for Zeeman Graphite Tube Analysers = USEPA SW-846 (PTO) = Continue on following page $For seawater, NH4NO3 is added to aid in the low temperature removal of NaCl by the formation of NH4Cl and NaNO3.

ELEMENT/SAMPLE/MMREMARKS



Blood, serum, urine






Soil





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04 Matrix Modifiers for Graphite Furnace Analysis