INDUCTIVELY COUPLED PLASMA/MASS SPECTROMETRY (3125)/ICP/MS Method 3-45

3125 METALS BY INDUCTIVELY COUPLED PLASMA/MASS SPECTROMETRY*

3125 A. Introduction

1. General Discussion 2. References

This method is used for the determination of trace metals 1. MONTASER, A. & D.W. GOLIGHTLY, eds. 1992. Inductively Coupled
and metalloids in surface, ground, and drinking waters by Plasmas in Analytical Atomic Spectrometry, 2nd ed. VCH Publish-
inductively coupled plasma/mass spectrometry (ICP/MS). It ers, Inc., New York, N.Y.
2. DATE, A.R. & A.L. GRAY. 1989. Applications of Inductively Coupled
may also be suitable for wastewater, soils, sediments, sludge,
Plasma Mass Spectrometry. Blackie & Son, Ltd., Glasgow, U.K.
and biological samples after suitable digestion followed by 3. U.S. ENVIRONMENTAL PROTECTION AGENCY. 1994. Determination of trace
dilution and/or cleanup.1,2 Additional sources of information elements in waters and wastes by inductively coupled plasma-mass
on quality assurance and other aspects of ICP/MS analysis of spectrometry, Method 200.8. U.S. Environmental Protection Agency,
metals are available.35 Environmental Monitoring Systems Lab., Cincinnati, Ohio.
The method is intended to be performance-based, allowing 4. LONGBOTTOM, J.E., T.D. MARTIN, K.W. EDGELL, S.E. LONG, M.R.
extension of the elemental analyte list, implementation of PLANTZ & B.E. WARDEN. 1994. Determination of trace elements in
clean preparation techniques as they become available, and water by inductively coupled plasma-mass spectrometry: collabo-
other appropriate modifications of the base method as tech- rative study. J. AOAC Internat. 77:1004.
5. U.S. ENVIRONMENTAL PROTECTION AGENCY. 1995. Method 1638: De-
nology evolves. Preferably validate modifications to the base
termination of trace elements in ambient waters by inductively
method by use of the quality control standards specified in the coupled plasma-mass spectrometry. U.S. Environmental Protection
method. Agency, Off. Water, Washington, D.C.
Instrument detection levels for many analytes are between 1 6. MCLAREN, J.W., A.P. MYKYTIUK, S.N. WILLIE & S. S. BERMAN. 1985.
and 100 ng/L. The method is best suited for the determination of Determination of trace metals in seawater by inductively coupled
metals in ambient or pristine fresh-water matrices. More com- plasma mass spectrometry with preconcentration on silica-immobi-
plex matrices may require some type of cleanup to reduce matrix lized 8-hydroxyquinoline. Anal. Chem. 57:2907.
effects to a manageable level. Various cleanup techniques are 7. BURBA, P. & P.G. WILLMER. 1987. Multielement preconcentration
for atomic spectroscopy by sorption of dithiocarbamate metal com-
available to reduce matrix interferences and/or concentrate ana-
plexes (e.g., HMDC) on cellulose collectors. Fresenius Z. Anal.
lytes of interest.6 10 Chem. 329:539.
This method is ideally used by analysts experienced in the use 8. WANG, X. & R.M. BARNES. 1989. Chelating resins for on-line flow
of ICP/MS, the interpretation of spectral and matrix interference, injection preconcentration with inductively coupled plasma atomic
and procedures for their correction. Preferably demonstrate an- emission spectroscopy. J. Anal. Atom. Spectrom. 4:509.
alyst proficiency through analysis of a performance evaluation 9. SIRIRAKS, A., H.M. KINGSTON & J.M. RIVIELLO. 1990. Chelation ion
sample before the generation of data. chromatography as a method for trace elemental analysis in com-
plex environmental and biological samples. Anal. Chem. 62:1185.
10. PUGET SOUND WATER QUALITY AUTHORITY. 1996. Recommended
Guidelines for Measuring Metals in Puget Sound Marine Water,
* Approved by Standard Methods Committee, 1997.
Joint Task Group: 20th EditionWilliam R. Kammin (chair), John R. Barnett,
Sediment and Tissue Samples. Appendix D: Alternate Methods for
Isabel C. Chamberlain, Robert Henry, James O. Ross, Ruth E. Wolf, Cindy A. the Analysis of Marine Water Samples. Puget Sound Water Quality
Ziernicki. Authority, Olympia, Wash.

3125 B. Inductively Coupled Plasma/Mass Spectrometry (ICP/MS) Method

1. General Discussion target elements. Ions generated by these energy-transfer pro-

cesses are extracted from the plasma through a differential
a. Principle: Sample material is introduced into an argon- vacuum interface, and separated on the basis of their mass-to-
based, high-temperature radio-frequency plasma, usually by charge ratio by a mass spectrometer. The mass spectrometer
pneumatic nebulization. Energy transfer from the plasma to the usually is of the quadrupole or magnetic sector type. The ions
sample stream causes desolvation, atomization, and ionization of passing through the mass spectrometer are counted, usually by
3-46 METALS (3000)

TABLE 3125:I. RECOMMENDED ANALYTE MASSES, INSTRUMENTAL ground analyte in metals preparation and analysis laboratories
DETECTION LEVELS (IDL), AND INTERNAL STANDARDS and matrix-based interferences. Determine both IDL and MDL
IDL* Recommended upon initial implementation of this method, and then yearly or
Element Analytical Mass g/L Internal Standard whenever the instrument configuration changes or major main-
tenance occurs, whichever comes first.
Be 9 0.025 Li Determine linear dynamic ranges (LDR) for all method ana-
Al 27 0.03 Sc lytes. LDR is defined as the maximum concentration of analyte
V 51 0.02 Sc above the highest calibration point where analyte response is
Cr 52 0.04 Sc
within 10% of the theoretical response. When determining
Cr 53 0.03 Sc
Mn 55 0.002 Sc linear dynamic ranges, avoid using unduly high concentrations
Co 59 0.002 Sc of analyte that might damage the detector. Determine LDR on
Ni 60 0.004 Sc multielement mixtures, to account for possible interelement ef-
Ni 62 0.025 Sc fects. Determine LDR on initial implementation of this method,
Cu 63 0.003 Sc and then yearly.
Cu 65 0.004 Sc c. Interferences: ICP/MS is subject to several types of inter-
Zn 66 0.017 Ge ferences.
Zn 68 0.020 Ge 1) Isotopes of different elements that form ions of the same
As 75 0.025 Ge nominal mass-to-charge ratio are not resolved by the quadrupole
Se 77 0.093 Ge
mass spectrometer, and cause isobaric elemental interferences.
Se 82 0.064 Ge
Ag 107 0.003 In Typically, ICP/MS instrument operating software will have all
Ag 109 0.002 In
Cd 111 0.006 In
Cd 114 0.003 In TABLE 3125:II. ELEMENTAL ABUNDANCE EQUATIONS AND COMMON
Sb 121 0.07 In MOLECULAR ION CORRECTION EQUATIONS
Sb 123 0.07 In
Tl 203 0.03 Th Elemental and Molecular Equations*
Tl 205 0.03 Th Li 6 C 6
Pb 208 0.005 Th Be 9 C 9
U 235 0.032 Th Al 27 C 27
U 238 0.001 Th Sc 45 C 45
Mo 98 0.003 In V 51 C 51 (3.127)[(C 53) (0.113 C 52)]
Ba 135 0.008 In Cr 52 C 52
Sr 88 0.001 In Cr 53 C 53
* IDLs were determined on a Perkin Elmer Elan 6000 ICP/MS using seven Mn 55 C 55
replicate analyses of a 1% nitric acid solution, at Manchester Environmental Co 59 C 59
Laboratory, July 1996. Ni 60 C 60
From EPA Method 200.8 for the Analysis of Drinking Waters-Application Note, Ni 62 C 62
Order No. ENVA-300A, The Perkin Elmer Corporation, 1996. Cu 63 C 63
From Perkin Elmer Technical Summary TSMS-12. Cu 65 C 65
Zn 66 C 66
Zn 68 C 68
an electron multiplier detector, and the resulting information As 75 C 75 (3.127)[(C 77) (0.815 C 82)]
Se 77 C 77
processed by a computer-based data-handling system.
Se 82 C 82 (1.008696 C 83)
b. Applicable elements and analytical limits: This method is Sr 88 C 88
suitable for aluminum, antimony, arsenic, barium, beryllium, Mo 98 C 98 (0.110588 C 101)
cadmium, chromium, cobalt, copper, lead, manganese, molyb- Rh 103 C 103
denum, nickel, selenium, silver, strontium, thallium, uranium, Ag 107 C 107
vanadium, and zinc. The method is also acceptable for other Ag 109 C 109
elemental analytes as long as the same quality assurance prac- Cd 111 C 111 (1.073)[(C 108) (0.712 C 106)]
tices are followed. The basic element suite and recommended Cd 114 C 114 (0.02686 C 118)
analytical masses are given in Table 3125:I. Sb 121 C 121
Typical instrument detection levels (IDL)1,2 for method ana- Sb 123 C 123 (0.127189 C 125)
Ba 135 C 135
lytes are presented in Table 3125:I. Determine the IDL and
Ho 165 C 165
method detection level (or limit) (MDL) for all analytes before Tl 203 C 203
method implementation. Section 1030 contains additional infor- Tl 205 C 205
mation and approaches for the evaluation of detection capabili- Pb 208 C 208 (1 C 206) (1 C 207)
ties. Th 232 C 232
The MDL is defined in Section 1010C and elsewhere.2 Deter- U 238 C 238
mination of the MDL for each element is critical for complex * C calibration blank corrected counts at indicated mass.
matrices such as seawater, brines, and industrial effluents. The From EPA Method 200.8 for the Analysis of Drinking Waters Application
MDL will typically be higher than the IDL, because of back- Note, Order No. ENVA-300A, The Perkin Elmer Corporation, 1996.
INDUCTIVELY COUPLED PLASMA/MASS SPECTROMETRY (3125)/ICP/MS Method 3-47

TABLE 3125:III. COMMON MOLECULAR ION INTERFERENCES IN ICP/MS1 known isobaric interferences entered, and will perform necessary
calculations automatically. Table 3125:II shows many of the
Element Measurement
Molecular Ion Mass Affected by Interference commonly used corrections. Monitor the following additional
masses: 83Kr, 99Ru, 118Sn, and 125Te. It is necessary to monitor
Background molecular ions: these masses to correct for isobaric interference caused by 82Kr
NH 15 on 82Se, by 98Ru on 98Mo, by 114Sn on 114Cd, and by 123Te on
OH 17 123
OH2 18
Sb. Monitor ArCl at mass 77, to estimate chloride interfer-
C2 24 Mg ences. Verify that all elemental and molecular correction equa-
CN 26 Mg tions used in this method are correct and appropriate for the mass
CO 28 Si spectrometer used and sample matrix.
N2 28 Si 2) Abundance sensitivity is an analytical condition in which
N2H 29 Si
NO 30 the tails of an abundant mass peak contribute to or obscure
NOH 31 P adjacent masses. Adjust spectrometer resolution to minimize
O2 32 S these interferences.
O2H 33 3) Polyatomic (molecular) ion interferences are caused by
36
ArH 37 Cl ions consisting of more than one atom and having the same
38
ArH 39 K
40
ArH 41 nominal mass-to-charge ratio as the isotope of interest. Most of
CO2 44 Ca the common molecular ion interferences have been identified
CO2H 45 Sc and are listed in Table 3125:III. Because of the severity of
ArC, ArO 52 Cr chloride ion interference on important analytes, particularly ar-
ArN 54 Cr senic and selenium, hydrochloric acid is not recommended for
ArNH 55 Mn
ArO 56 Fe use in preparation of any samples to be analyzed by ICP/MS.
ArH 57 Fe The mathematical corrections for chloride interferences only
40
Ar36Ar 76 Se correct chloride to a concentration of 0.4%. Because chloride ion
40
Ar38Ar 78 Se is present in most environmental samples, it is critical to use
40
Ar2 80 Se
Matrix molecular ions:
chloride correction equations for affected masses. A high-reso-
Bromide: lution ICP/MS may be used to resolve interferences caused by
81
BrH 82 Se polyatomic ions. Polyatomic interferences are strongly influ-
79
BrO 95 Mo enced by instrument design and plasma operating conditions, and
81
BrO 97 Mo can be reduced in some cases by careful adjustment of nebulizer
81
BrOH 98 Mo
Ar81Br 121 Sb gas flow and other instrument operating parameters.
Chloride: 4) Physical interferences include differences in viscosity, sur-
35
ClO 51 V face tension, and dissolved solids between samples and calibra-
35
ClOH 52 Cr tion standards. To minimize these effects, dissolved solid levels
37
ClO 53 Cr in analytical samples should not exceed 0.5%. Dilute water and
37
ClOH 54 Cr
Ar35Cl 75 As wastewater samples containing dissolved solids at or above 0.5%
Ar37Cl 77 Se before analysis. Use internal standards for correction of physical
Sulfate: interferences. Any internal standards used should demonstrate com-
32
SO 48 Ti parable analytical behavior to the elements being determined.
32
SOH 49 5) Memory interferences occur when analytes from a previ-
34
SO 50 V, Cr
34
SOH 51 V ous sample or standard are measured in the current sample. Use
SO2, S2 64 Zn a sufficiently long rinse or flush between samples to minimize
Ar32S 72 Ge this type of interference. If memory interferences persist, they
Ar34S 74 Ge may be indications of problems in the sample introduction sys-
Phosphate: tem. Severe memory interferences may require disassembly and
PO 47 Ti
POH 48 Ti cleaning of the entire sample introduction system, including the
PO2 63 Cu plasma torch, and the sampler and skimmer cones.
ArP 71 Ga 6) Ionization interferences result when moderate (0.1 to 1%)
Group I & II metals: amounts of a matrix ion change the analyte signal. This effect,
ArNa 63 Cu
ArK 79 Br
which usually reduces the analyte signal, also is known as
ArCa 80 Se suppression. Correct for suppression by use of internal stan-
Matrix oxides* dardization techniques.
TiO 6266 Ni, Cu, Zn
ZrO 106112 Ag, Cd 2. Apparatus
MoO 108116 Cd
NbO 109 Ag
a. Inductively coupled plasma/mass spectrometer: Instrumen-
* Oxide interferences normally will be very small and will affect the method elements tation, available from several manufacturers, includes a mass
only when oxide-producing elements are present at relatively high concentrations, or
when the instrument is improperly tuned or maintained. Preferably monitor Ti and Zr
spectrometer detector, inductively coupled plasma source, mass
isotopes for soil, sediment, or solid waste samples, because these samples potentially flow controllers for regulation of ICP gas flows, peristaltic pump
contain high levels of these interfering elements. for sample introduction, and a computerized data acquisition and
3-48 METALS (3000)

instrument control system. An x-y autosampler also may be used c. Stock, standard, and other required solutions: See
with appropriate control software. 3120B.3d for preparation of standard stock solutions from ele-
b. Laboratory ware: Use precleaned plastic laboratory ware mental materials (pure metals, salts). Preferably, purchase high-
for standard and sample preparation. Teflon,* either tetrafluoro- purity commercially prepared stock solutions and dilute to re-
ethylene hexafluoropropylene-copolymer (FEP), polytetrafluo- quired concentrations. Single- or multi-element stock solutions
roethylene (PTFE), or perfluoroalkoxy PTFE (PFA) is preferred (1000 mg/L) of the following elements are required: aluminum,
for standard preparation and sample digestion, while high-density antimony, arsenic, barium, beryllium, cerium, cadmium, chro-
polyethylene (HDPE) and other dense, metal-free plastics may be mium, cobalt, copper, germanium, indium, lead, magnesium,
acceptable for internal standards, known-addition solutions, etc. manganese, molybdenum, nickel, rhodium, scandium, selenium,
Check each new lot of autosampler tubes for suitability, and pre- silver, strontium, terbium, thallium, thorium, uranium, vana-
clean autosampler tubes and pipettor tips (see Section 3010C.2). dium, and zinc. Prepare internal standard stock separately from
c. Air displacement pipets, 10 to 100 L, 100 to 1000 L, and target element stock solution. The potential for incompatibility
1 to 10 mL size. between target elements and/or internal standards exists, and
d. Analytical balance, accurate to 0.1 mg. could cause precipitation or other solution instability.
e. Sample preparation apparatus, such as hot plates, micro- 1) Internal standard stock solution: Lithium, scandium, ger-
wave digestors, and heated sand baths. Any sample preparation manium, indium, and thorium are suggested as internal stan-
device has the potential to introduce trace levels of target ana- dards. The following masses are monitored: 6Li, 45Sc, 72Ge,
115
lytes to the sample. In, and 232Th. Add to all samples, standards, and quality
f. Clean hood (optional), Class 100 (certified to contain less control (QC) samples a level of internal standard that will give a
than 100 particles/m3), for sample preparation and manipulation. suitable counts/second (cps) signal (for most internal standards,
Preferably perform all sample manipulations, digestions, dilu- 200 000 to 500 000 cps; for lithium, 20 000 to 70 000 cps).
tions, etc. in a certified Class 100 environment. Alternatively, Minimize error introduced by dilution during this addition by
handle samples in glove boxes, plastic fume hoods, or other using an appropriately high concentration of internal standard
environments where random contamination by trace metals can mix solution. Maintain volume ratio for all internal standard
be minimized. additions.
Prepare internal standard mix as follows: Prepare a nominal
3. Reagents 50-mg/L solution of 6Li by dissolving 0.15 g 6Li2CO3 (isotopi-
cally pure, i.e., 95% or greater purity) in a minimal amount of
a. Acids: Use ultra-high-purity grade (or equivalent) acids to 1:1 HNO3. Pipet 5.0 mL 1000-mg/L scandium, germanium,
prepare standards and to process sample. Redistilled acids are indium, and thorium standards into the lithium solution, dilute
acceptable if each batch is demonstrated to be free from con- resulting solution to 500.0 mL, and mix thoroughly. The result-
tamination by target analytes. Use extreme care in the handling ant concentration of Sc, Ge, In, and Th will be 10 mg/L. Older
of acids in the laboratory to avoid contamination of the acids instruments may require higher levels of internal standard to
with trace levels of metals. achieve acceptable levels of precision.
1) Nitric acid, HNO3, conc (specific gravity 1.41). Other internal standards, such as rhodium, yttrium, terbium,
2) Nitric acid, 1 1: Add 500 mL conc HNO3 to 500 mL holmium, and bismuth may also be used in this method. Ensure
reagent water. that internal standard mix used is stable and that there are no
3) Nitric acid, 2%: Add 20 mL conc HNO3 to 100 mL reagent undesired interactions between elements.
water; dilute to 1000 mL. Screen all samples for internal standard elements before anal-
4) Nitric acid, 1%: Add 10 mL conc HNO3 to 100 mL reagent ysis. The analysis of a few representative samples for internal
water; dilute to 1000 mL. standards should be sufficient. Analyze samples as received or
b. Reagent water: Use water of the highest possible purity for as digested (before addition of internal standard), then add
blank, standard, and sample preparation (see Section 1080). internal standard mix and reanalyze. Monitor counts at the in-
Alternatively, use the procedure described below to produce ternal standard masses. If the as received or as digested
water of acceptable quality. Other water preparation regimes samples show appreciable detector counts (10% or higher of
may be used, provided that the water produced is metal-free. samples with added internal standard), dilute sample or use an
Reagent water containing trace amounts of analyte elements will alternate internal standard. If the internal standard response of
cause erroneous results. the sample with the addition is not within 70 to 125% of the
Produce reagent water using a softener/reverse osmosis unit response for a calibration blank with the internal standard added,
with subsequent UV sterilization. After the general deionization either dilute the sample before analysis, or use an alternate
system use a dual-column strong acid/strong base ion exchange internal standard. During actual analysis, monitor internal stan-
system to polish laboratory reagent water before production of dard masses and note all internal standard recoveries over 125%
metal-free water. Use a multi-stage reagent water system, with of internal standard response in calibration blank. Interpret re-
two strong acid/strong base ion exchange columns and an acti- sults for these samples with caution.
vated carbon filter for organics removal for final polishing of The internal standard mix may be added to blanks, standards,
laboratory reagent water. Use only high-purity water for prepa- and samples by pumping the solution so it is mixed with the
ration of samples and standards. sample stream in the sample introduction process.

* Or equivalent. Cambridge Isotope Laboratories or equivalent.

INDUCTIVELY COUPLED PLASMA/MASS SPECTROMETRY (3125)/ICP/MS Method 3-49

TABLE 3125:IV. SUGGESTED ANALYTICAL RUN SEQUENCE 2) Instrument optimization/tuning solution, containing the
following elements: barium, beryllium, cadmium, cerium, co-
Sample Type Comments
balt, copper, germanium, indium, magnesium, rhodium, scan-
Tuning/optimization standard Check mass calibration and dium, terbium, thallium, and lead. Prepare this solution in 2%
resolution HNO3. This mix includes all common elements used in optimi-
Tuning/optimization standard Optimize instrument for maximum zation and tuning of the various ICP/MS operational parameters.
rhodium counts while keeping It may be possible to use fewer elements in this solution, de-
oxides, double charged ions, pending on the instrument manufacturers recommendations.
and background within
3) Calibration standards, 0, 5, 10, 20, 50, and 100 g/L.
instrument specifications
Rinse Other calibration regimes are acceptable, provided the full suite
Reagent blank Check for contamination of quality assurance samples and standards is run to validate
Reagent blank Calibration standard blank these method changes. Fewer standards may be used, and a
5-g/L standard two-point blank/mid-range calibration technique commonly used
10-g/L standard in ICP optical methods should also produce acceptable results.
20-g/L standard Calibrate all analytes using the selected concentrations. Prepare
50-g/L standard all calibration standards and blanks in a matrix of 2% nitric acid.
100-g/L standard Add internal standard mix to all calibration standards to provide
Rinse appropriate count rates for interference correction. NOTE: All
Initial calibration verification, 50
standards and blanks used in this method have the internal
g/L
Initial calibration blank standard mix added at the same ratio.
0.30-g/L standard Low-level calibration verification 4) Method blank, consisting of reagent water ( 3b) taken
1.0-g/L standard Low-level calibration verification through entire sample preparation process. For dissolved sam-
External reference material NIST 1643c or equivalent ples, take reagent water through same filtration and preservation
Continuing calibration verification processes used for samples. For samples requiring digestion,
Continuing blank calibration process reagent water with the same digestion techniques as
Project sample method blank samples. Add internal standard mix to method blank.
Project sample laboratory-fortified
blank
Project sample 14
Project sample 5 Performance data for the method were obtained with these concentrations.
Project sample 5 with known
addition
Project sample 5 duplicate with TABLE 3125:VI. QUALITY CONTROL ANALYSES FOR ICP/MS METHOD
known addition Analysis Frequency Acceptance Criteria
Continuing calibration verification
Continuing calibration blank Reference material Greater of: once Dependent on data
[3c9)] per sample quality objectives
batch, or 5%
Preparatory/method Greater of: once Absolute value
blank [ 3c4)] per sample of instrument
TABLE 3125:V. SUMMARY OF PERFORMANCE CRITERIA batch, or 5% detection limit;
Performance Characteristic Criteria absolute value
of laboratory
Mass resolution Manufacturers specification reporting limit or
Mass calibration Manufacturers specification MDL is
Ba2/Ba Manufacturers specification acceptable
CeO/Ce Manufacturers specification Laboratory fortified Greater of: once 30% of true
Background counts at mass 220 Manufacturers specification blank [ 3c7)] per sample value
Correlation coefficient 0.995 batch, or 5%
Calibration blanks Reporting limit Duplicate known- Greater of: once 20% relative
Calibration verification standards 10% of true value addition samples per sample percent
Laboratory fortified blank (control batch, or 5% difference
sample) 30% of true value Continuing calibration 10% 10% of known
Precision 20% relative percent difference verification standards concentration
for lab duplicates [ 3c5)]
Known-addition recovery 75125% Continuing calibration 10% Absolute value
0.3 and 1.0 g/L standards Dependent on data quality verification blank of instrument
objectives [ 3c6)] detection limit;
Reference materials Dependent on data quality absolute value
objectives of laboratory
Internal standard response 70125% of response in reporting limit or
calibration blank with known MDL is
addition acceptable
3-50 METALS (3000)

TABLE 3125:VII. METHOD PERFORMANCE WITH CALIBRATION VERIFICATION STANDARDS*

Continuing Calibration Verification Standard (N 44) Initial Calibration Verification Standard (N 12)
Standard Relative Standard Standard Relative Standard
Mean Recovery Mean Deviation Deviation Mean Recovery Mean Deviation Deviation
Element Mass % g/L g/L % % g/L g/L %

Be 9 98.71 49.35 3.43 6.94 100.06 50.03 1.90 3.80

Al 27 99.62 49.81 2.99 6.01 98.42 49.21 1.69 3.44
V 51 100.97 50.48 1.36 2.68 99.91 49.96 1.23 2.47
Cr 52 101.39 50.70 1.86 3.66 99.94 49.97 1.47 2.95
Cr 53 100.68 50.34 1.91 3.79 99.13 49.56 1.44 2.90
Mn 55 101.20 50.60 1.98 3.91 99.48 49.74 1.40 2.82
Co 59 101.67 50.83 2.44 4.79 99.44 49.72 1.61 3.24
Ni 60 99.97 49.99 2.14 4.28 97.98 48.99 1.70 3.47
Ni 62 99.79 49.89 2.09 4.18 97.57 48.79 1.32 2.71
Cu 63 100.51 50.25 2.19 4.36 97.87 48.93 1.63 3.33
Cu 65 100.39 50.19 2.26 4.51 98.34 49.17 1.58 3.20
Zn 66 101.07 50.53 1.93 3.82 98.75 49.38 0.87 1.76
Zn 68 100.42 50.21 1.89 3.77 97.75 48.87 0.50 1.02
As 75 100.76 50.38 1.15 2.28 98.83 49.41 0.89 1.80
Se 77 101.71 50.85 1.43 2.81 99.54 49.77 1.01 2.03
Se 82 101.97 50.98 1.50 2.95 99.76 49.88 0.94 1.89
Ag 107 101.50 50.75 1.68 3.30 99.27 49.63 1.17 2.36
Ag 109 101.65 50.83 1.68 3.31 99.66 49.83 1.54 3.08
Cd 111 100.92 50.46 1.94 3.84 98.61 49.30 1.36 2.77
Cd 114 100.90 50.45 2.07 4.10 99.20 49.60 1.41 2.84
Sb 121 100.14 50.07 2.39 4.77 99.38 49.69 1.38 2.78
Sb 123 99.98 49.99 2.48 4.97 99.09 49.54 1.34 2.71
Tl 203 101.36 50.68 1.64 3.23 100.05 50.02 1.01 2.01
Tl 205 102.40 51.20 1.93 3.78 101.23 50.62 1.45 2.87
Pb 208 101.21 50.61 1.65 3.25 99.33 49.67 0.84 1.69
U 238 101.54 50.77 1.93 3.80 99.80 49.90 1.36 2.72
* Single-laboratory, single-operator, single-instrument data, determined using a 50-g/L standard prepared from sources independent of calibration standard source. Data
acquired January-November 1996 during actual sample determinations. Performance of continuing calibration verification standards at different levels may vary.
Perkin-Elmer Elan 6000 ICP/MS used for determination.

5) Calibration verification standard: Prepare a mid-range d. Argon: Use a prepurified grade of argon unless it can be
standard, from a source different from the source of the calibra- demonstrated that other grades can be used successfully. The use
tion standards, in 2% HNO3, with equivalent addition of internal of prepurified argon is usually necessary because of the presence
standard. of krypton as an impurity in technical argon. 82Kr interferes with
6) Calibration verification blank: Use 2% HNO3. the determination of 82Se. Monitor 83Kr at all times.
7) Laboratory fortified blank (optional): Prepare solution with
2% nitric acid and method analytes added at about 50 g/L. This
standard, sometimes called a laboratory control sample (LCS), is 4. Procedures
used to validate digestion techniques and known-addition levels.
8) Reference materials: Externally prepared reference mate- a. Sample preparation: See Sections 3010 and 3020 for general
rial, preferably from National Institute of Standards and Tech- guidance regarding sampling and quality control. See Section
nology (NIST) 1643 series or equivalent. 3030E for recommended sample digestion technique for all analytes
9) Known-addition solution for samples: Add stock standard except silver and antimony. If silver and antimony are target ana-
to sample in such a way that volume change is less than 5%. In lytes, use method given in 3030F, paying special attention to inter-
the absence of information on analyte levels in the sample, ferences caused by chloride ion, and using all applicable elemental
prepare known additions at around 50 g/L. If analyte concen- corrections. Alternative digestion techniques and additional guid-
tration levels are known, add at 50 to 200% of the sample levels. ance on sample preparation are available.3,4
For samples undergoing digestion, make additions before diges- Ideally use a clean environment for any sample handling,
tion. For the determination of dissolved metals, make additions manipulation, or preparation. Preferably perform all sample ma-
after filtration, preferably immediately before analysis. nipulations in a Class 100 clean hood or room to minimize
10) Low-level standards: Use both a 0.3- and a 1.0-g/L potential contamination artifacts in digested or filtered samples.
standard when expected analyte concentration is below 5 g/L. b. Instrument operating conditions: Follow manufacturers
Prepare both these standards in 2% nitric acid. standard operating procedures for initialization, mass calibration,
Prepare volumetrically a mixed standard containing the gas flow optimization, and other instrument operating condi-
method analytes at desired concentration(s) (0.30 g/L, 1.0 tions. Maintain complete and detailed information on the oper-
g/L, or both). Prepare weekly in 100-mL quantities. ational status of the instrument whenever it is used.
INDUCTIVELY COUPLED PLASMA/MASS SPECTROMETRY (3125)/ICP/MS Method 3-51

c. Analytical run sequence: A suggested analytical run se- Immediately after calibration, run initial calibration verifica-
quence, including instrument tuning/optimization, checking of tion standard, 3c5); acceptance criteria are 10% of known
reagent blanks, instrument calibration and calibration verifica- analyte concentration. Next run initial calibration verification
tion, analysis of samples, and analysis of quality control samples blank, 3c6); acceptance criteria are ideally the absolute value
and blanks, is given in Table 3125:IV. of the instrument detection limit for each analyte, but in practice,
d. Instrument tuning and optimization: Follow manufactur- the absolute value of the laboratory reporting limit or the
ers instructions for optimizing instrument performance. The laboratory method detection limit for each analyte is acceptable.
most important optimization criteria include nebulizer gas flows, Verify low-level calibration by running 0.3- and/or 1.0-g/L
detector and lens voltages, radio-frequency forward power, and standards, if analyte concentrations are less than 5 g/L.
mass calibration. Periodically check mass calibration and instru- f. Sample analysis: Ensure that all vessels and reagents are
ment resolution. Ideally, optimize the instrument to minimize free from contamination. During analytical run (see Table 3125:
oxide formation and doubly-charged species formation. Measure IV), include quality control analyses according to schedule of
the CeO/Ce ratio to monitor oxide formation, and measure Table 3125:VI, or follow project-specific QA/QC protocols.
doubly-charged species by determination of the Ba2/Ba ratio. Internal standard recoveries must be between 70% and 125% of
Both these ratios should meet the manufacturers criteria before internal standard response in the laboratory-fortified blank; other-
instrument calibration. Monitor background counts at mass 220 wise, dilute sample, add internal standard mix, and reanalyze.
after optimization and compare with manufacturers criteria. A Make known-addition analyses for each separate matrix in a
summary of performance criteria related to optimization and digestion or filtration batch.
tuning, calibration, and analytical performance for this method is
given in Table 3125:V.
e. Instrument calibration: After optimization and tuning, cal- 5. Calculations and Corrections
ibrate instrument using an appropriate range of calibration stan-
dards. Use appropriate regression techniques to determine cali- Configure instrument software to report internal standard cor-
bration lines or curves for each analyte. For acceptable calibra- rected results. For water samples, preferably report results in
tions, correlation coefficients for regression curves are ideally micrograms per liter. Report appropriate number of significant
0.995 or greater. figures.

TABLE 3125:VIII. METHOD PERFORMANCE FOR RECOVERY OF KNOWN ADDITION IN NATURAL WATERS*
Total Recoverable Metals Dissolved Metals
Relative Standard Relative Standard
Mean Recovery Deviation Mean Recovery Deviation
Element Mass % % % %

Be 9 89.09 5.77
V 51 87.00 8.82
Cr 52 87.33 8.42 88.38 6.43
Cr 53 86.93 7.90 88.52 5.95
Mn 55 91.81 10.12
Co 59 87.67 8.92
Ni 60 85.07 8.42 89.31 5.70
Ni 62 84.67 8.21 89.00 5.82
Cu 63 84.13 8.46 88.55 8.33
Cu 65 84.37 8.05 88.26 7.80
Zn 66 86.14 23.01 95.59 13.81
Zn 68 81.95 20.31 91.94 13.27
As 75 90.43 4.46 97.30 8.84
Se 77 83.09 4.76 105.36 10.80
Se 82 83.42 4.73 105.36 10.75
Ag 107 91.98 5.06
Ag 109 92.25 4.96
Cd 111 91.37 5.47 96.91 6.03
Cd 114 91.47 6.04 97.03 5.42
Sb 121 94.40 5.24
Sb 123 94.56 5.36
Tl 203 97.24 5.42
Tl 205 98.14 6.21
Pb 208 96.09 7.08 100.69 7.28
* Single-laboratory, single-operator, single-instrument data. Samples were Washington State surface waters from various locations. Data acquired January-November 1996
during actual sample determinations. Performance of known additions at different levels may vary. Perkin-Elmer Elan 6000 ICP/MS used for determination.
Known-addition level 20 g/L. Additions made before preparation according to Section 3030E (modified by cleanhood digestion in TFE beakers). N 20.
Known-addition level for Cd and Pb 1 g/L; for other analytes 10 g/L. Additions made after filtration through 1:1 HNO3 precleaned 0.45-m filters. N 28.
3-52 METALS (3000)

TABLE 3125:IX. METHOD PERFORMANCE WITH LOW-LEVEL CHECK STANDARDS*

1.0-g/L Standard 0.3-g/L Standard
Mean Standard Relative Standard Mean Standard Relative Standard
Recovery Mean Deviation Deviation Recovery Mean Deviation Deviation
Element Mass % g/L g/L % % g/L g/L %

Be 9 97 0.97 0.06 6.24 95 0.284 0.03 12.11

Al 27 121 1.21 0.32 26.49 196 0.588 0.44 74.30
V 51 104 1.04 0.06 5.83 111 0.332 0.10 28.96
Cr 52 119 1.19 0.34 28.62 163 0.490 0.37 75.90
Cr 53 102 1.02 0.36 35.54 113 0.338 0.32 93.70
Mn 55 103 1.03 0.07 6.55 110 0.329 0.08 25.64
Co 59 103 1.03 0.07 6.42 102 0.307 0.04 12.53
Ni 60 101 1.01 0.05 5.24 107 0.321 0.05 14.14
Ni 62 102 1.02 0.06 5.42 109 0.326 0.05 15.94
Cu 63 107 1.07 0.09 8.78 118 0.355 0.06 18.29
Cu 65 107 1.07 0.10 9.05 117 0.352 0.06 17.69
Zn 66 117 1.17 0.51 43.52 182 0.547 0.68 124.13
Zn 68 116 1.16 0.50 42.90 179 0.537 0.66 122.12
As 75 97 0.97 0.05 5.23 101 0.302 0.06 18.29
Se 77 89 0.89 0.08 8.72 88 0.265 0.08 29.07
Se 82 92 0.92 0.14 15.50 106 0.317 0.14 43.91
Ag 107 101 1.01 0.05 4.53 94 0.282 0.04 15.74
Ag 109 103 1.03 0.07 6.57 92 0.277 0.04 13.68
Cd 111 98 0.98 0.04 3.80 96 0.288 0.03 8.74
Cd 114 100 1.00 0.03 3.39 98 0.293 0.03 8.70
Sb 121 94 0.94 0.05 5.28 93 0.280 0.06 21.89
Sb 123 94 0.94 0.05 5.36 93 0.278 0.06 22.39
T1 203 101 1.01 0.04 3.57 98 0.294 0.03 11.89
Tl 205 104 1.04 0.05 5.15 100 0.300 0.03 10.43
Pb 208 104 1.04 0.04 3.65 104 0.312 0.03 11.13
U 238 106 1.06 0.05 4.64 102 0.307 0.03 9.92
* Single-laboratory, single-operator, single-instrument data. N 24 for both standards.

a. Correction for dilutions and solids: Correct all results for laboratory blank. For regulatory programs, ensure that reporting
dilutions, and raise reporting limit for all analytes reported from limits for method analytes are a factor of three below relevant
the diluted sample by a corresponding amount. Similarly, if regulatory criteria.
results for solid samples are to be determined, use Method If method blank contamination is typically random, sporadic,
2540B to determine total solids. Report results for solid samples or otherwise not in statistical control, do not correct results for
as micrograms per kilogram, dry weight. Correct all results for the method blank. Consider the correction of results for labora-
solids content of solid samples. Use the following equation to tory method blanks only if it can be demonstrated that the
correct solid or sediment sample results for dilution during concentration of analytes in the method blank is within statistical
digestion and moisture content: control over a period of months. Report all method blank data
explicitly in a manner identical to sample reporting procedures.
R uncorr V d. Documentation: Maintain documentation for the following
R corr (where applicable): instrument tuning, mass calibration, calibra-
W % TS/100
tion verification, analyses of blanks (method, field, calibration,
where: and equipment blanks), IDL and MDL studies, analyses of
samples and duplicates with known additions, laboratory and
Rcorr corrected result, g/kg,
field duplicate information, serial dilutions, internal standard
Runcorr uncorrected elemental result, g/L,
recoveries, and any relevant quality control charts.
V volume of digestate (after digestion), L,
W mass of the wet sample, kg, and
Also maintain, and keep available for review, all raw data
% TS percent total solids determined in the solid sample. generated in support of the method.5

b. Compensation for interferences: Use instrument software

to correct for interferences listed previously for this method. See 6. Method Performance
Table 3125:III for a listing of the most common molecular ion
interferences. Table 3125:I presents instrument detection limit (IDL) data
c. Data reporting: Establish appropriate reporting limits for generated by this method; this represents optimal state-of-the-
method analytes based on instrument detection limits and the art instrument detection capabilities, not recommended
ANODIC STRIPPING VOLTAMMETRY (3130)/Introduction 3-53

method detection or reporting limits. Tables 3125:VII through for mass spectrometric determination of trace elements. Anal.
IX contain single-laboratory, single-operator, single-instru- Chem. 52:2283.
ment performance data generated by this method for calibra- DOUGLAS, D.J. & J.B. FRENCH. 1981. Elemental analysis with a micro-
tion verification standards, low-level standards, and known- wave-induced plasma/quadrupole mass spectrometer system. Anal.
addition recoveries for fresh-water matrices. Performance Chem. 53:37.
HOUK, R.S., V.A. FASSEL & H.J. SVEC. 1981. Inductively coupled plas-
data for this method for some analytes are not currently
ma-mass spectrometry: Sample introduction, ionization, ion extrac-
available. However, performance data for similar ICP/MS tion and analytical results. Dyn. Mass Spectrom. 6:234.
methods are available in the literature.1,4 OLIVARES, J.A. & R.S. HOUK. 1985. Ion sampling for inductively coupled
plasma mass spectrometry. Anal. Chem. 57:2674.
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nati, Ohio. VAUGHAN, M.A. & G. HORLICK. 1986. Oxide, hydroxide, and doubly
2. U.S. ENVIRONMENTAL PROTECTION AGENCY. 1984. Definition and pro- charged analyte species in inductively coupled plasma/mass spec-
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