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Susitna-Watana Hydroelectric Project Document
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Title:
Appendix to Method 1631 : total mercury in tissue, sludge, sediment, and
soil by acid digestion and BrCl oxidation
SuWa 191
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U.S. Environmental Protection Agency, Office of Water
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Susitna-Watana Hydroelectric Project document number 191
Existing numbers on document:
EPA-821-R-01-013
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[Anchorage : Susitna-Watana Hydroelectric Project, 2013]
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January 2001 (original date)
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13 p.
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Notes:
Reissued online for the Susitna-Watana Hydroelectric Project in 2013. Originally published:
[Washington, D.C.] : U.S. Environmental Protection Agency, Office of Water, 2001.
All reports in the Susitna-Watana Hydroelectric Project Document series include an ARLIS-
produced cover page and an ARLIS-assigned number for uniformity and citability. All reports
are posted online at http://www.arlis.org/resources/susitna-watana/
EPA-821-R-01-013
January 2001
Appendix to Method 1631
Total Mercury in Tissue, Sludge, Sediment, and Soil
by Acid Digestion and BrCl Oxidation
1 Based on a standard operating procedure provided by Frontier Geosciences, Inc.
2
Appendix to Method 1631
Total Mercury in Tissue, Sludge, Sediment, and Soil
by Acid Digestion and BrCl Oxidation1
A1.0 Scope and Application
A1.1 This Appendix provides two sample preparation (digestion) procedures for oxidation of total
mercury (Hg) in solid and semi-solid sample matrices. These procedures may be used in conjunction
with EPA Method 1631B: Mercury in Water by Oxidation, Purge and Trap, and Cold Vapor
Atomic Fluorescence Spectrometry for determination of mercury in tissue, sludge, sediment, soil,
industrial samples, and certified reference materials.
A1.2 The digestion procedures in this Appendix, in conjunction with Method 1631B, allow determination
of Hg at concentrations ranging from 1.0 to 5000 ng/g in solid and semi-solid matrices. Higher
concentrations can be measured by selection of a smaller sample size and/or dilution of the digestate.
A1.3 The detection limit and minimum level of quantitation in this Method usually are dependent on the
level of interferences rather than instrumental limitations. The method detection limit (MDL; 40
CFR 136, Appendix B) for Hg has been determined to be in the range of 0.24 to 0.48 ng/g when no
interferences are present (see Appendix Tables A3 and A4). The minimum level of quantitation
(ML) has been established as 1.0 ng/g. These levels assume a sample size of 0.5 g.
A1.4 Because Hg concentrations in solids are typically 103 - 107 times higher than those found in aqueous
samples, the sensitivity provided by the dual amalgam trap system and fluorescence detector
described in Method 1631B may be more sensitive than necessary, and a single trap and/or cold
vapor atomic absorption spectroscopy (CVAAS) instrument may be adequate. These modifications
are allowed under the equivalency provisions in EPA Method 1631B. See Method 1631B Section
9.1.2. However, the dual amalgam trap system and fluorescence detector provide greater sensitivity
and specificity in the presence of interferences, and this system must be used to overcome
interferences, if present, and to achieve the sensitivity required, if necessary.
A2.0 Summary
A2.1 Digestion I—This procedure is preferred for matrices containing organic materials, such as sludge
and plant and animal tissues, because the organic matter is completely destroyed. In this procedure,
a 0.2 - 1.5 g sample is digested with HNO3/H2SO4. The digestate is diluted with BrCl solution to
destroy the remaining organic material.
A2.2 Digestion II—This procedure is preferred for geological materials because of rapid and complete
dissolution of cinnabar (HgS), which is otherwise more slowly attacked by the BrCl in Digestion I.
In this procedure, a 0.5 - 1.5 g sample is digested with aqua regia (HCl/HNO3) to solubilize
inorganic materials.
A2.3 The Hg concentration in the digestate is determined using EPA Method 1631B.
3
A3.0 Definitions
See the Glossary at the end of Method 1631B for definitions of the terms used in this Appendix.
A4.0 Contamination and Interferences
A4.1 For the complete recovery of mercury by Method 1631B, all Hg in the sample must be converted to
Hg(II). This is accomplished by free halogens present in the digestion step.
A4.2 In Digestion I, the addition of BrCl to the sample after it is fully solubilized HNO3/H2SO4 is critical
to convert methyl Hg to Hg(II). If the acid digestates are analyzed by Method 1631B without BrCl
oxidation of tissues or geological media, a significant low bias may occur.
A4.3 In Digestion II, the reaction between concentrated HCl and HNO3 in aqua regia generates nitrosyl
chloride (NOCl) and free Cl2, both of which are very strong oxidants for Hg-containing compounds
including cinnabar (HgS) and precious metal amalgams that are not attacked by either acid alone.
Aqua regia also converts all methyl Hg to Hg(II). The aqua regia procedure in Digestion II leaches
but does not dissolve silicate minerals. Crustal elements such as Fe, Al, Cr, Ba, and Si may not be
quantitatively recovered in some media using this procedure.
A4.4 Digestates from both Digestion I and II contain free halogens and extreme caution must be taken to
avoid purging these free halogens onto the gold sand traps (see Section 4.4.2 in Method 1631B).
Introduction of free halogens may be avoided by analyzing an aliquot of the sample digestate smaller
than 5 mL (Appendix Section A12.3), and by pipetting aliquots of the digestate into bubbler water
already containing SnCl2. The use of hydroxylamine hydrochloride to remove free halogens (as
prescribed in Method 1631B for aqueous samples) is not needed for solid sample digestates; there is
a sufficient amount of SnCl2 in the bubbler to reduce both Hg(II) and free halogens in digestate
aliquots smaller than 5 mL.
A4.5 If iodized coal or other elemental carbon samples are to be analyzed, the final acid concentration in
the diluted sample must be greater than 40% (v/v), and all carbon particles must be settled prior to
analysis to avoid re-adsorption of Hg on the carbon and an ensuing low bias.
A5.0 Safety
Observe the safety precautions in Method 1631B.
A6.0 Apparatus and Materials
A6.1 Digestion vessel—50-mL borosilicate Erlenmeyer flask, calibrated to 40 ± 0.5 mL; or any other
acid-cleaned, flat-bottomed, borosilicate glass container calibrated to 40 ± 0.5 mL.
A6.2 Pressure release digestion cap—Clear glass sphere or inverted fluoropolymer cone, approximately
1.5 - 2.0 cm in diameter, initially cleaned by heating overnight in hot concentrated nitric acid. The
sphere or cone acts as a pressure release valve during gas evolution. A common clear glass marble
may be used as the sphere, or the cone may be custom manufactured. Colored glass marbles contain
high levels of trace metals and must not be used. The cap must completely cover the opening of the
digestion vessel without falling in, yet not be so large as to risk falling off when slightly lifted by the
gas pressure in the vessel.
4
A6.3 Electric hot plate—A temperature controlled electric hot-plate capable of maintaining a temperature
of 100-110EC. A commonly available fluoropolymer-coated pancake griddle is excellent for this
purpose. Do not use the griddle for heating flammable solvents.
A6.4 Dilution vessels—Volumetric flasks, glass, 25, 50.0, and 100.0 mL, cleaned per the procedures in
Method 1631B.
A6.5 Digestate storage vessel—VOA vial, glass, 40-mL, with fluoropolymer-lined cap, cleaned per the
procedures in Method 1631B, or purchase I-Chem level 300, trace metal clean, with fluoropolymer-
lined cap, or equivalent.
A6.6 Balance—Analytical, capable of weighing 1.0 mg.
A7.0 Reagents and Standards
A7.1 Reference matrices
A7.1.1 Biota, including tissue and wet and dry municipal sludge—Chicken breast, skinless,
boneless, purchased at a local supermarket, or other tissue demonstrated to be free of
mercury at the MDL in Table A1.
A7.1.2 Soil, sediment, and other geological samples—Playground sand or other sand-like
material demonstrated to be free from mercury at the MDL in Table A1.
A7.2 Nitric acid (concentrated)—Reagent grade, containing less than 5 pg/mL Hg. The HNO3 must be
pre-analyzed for Hg before use.
A7.3 Sulfuric acid (concentrated)—Reagent grade, containing less than 5 pg/mL Hg. The H2SO4 must be
pre-analyzed for Hg before use.
A7.4 HNO3/H2SO4 solution—In a fume hood, slowly add 300 mL of concentrated H2SO4 (Appendix
Section A7.3) to 700 mL of concentrated HNO3 (Appendix Section A7.2) in a fluoropolymer bottle.
Warning: This mixture gets hot and emits caustic fumes.
A7.5 Dilute BrCl solutions—Use the concentrated (0.2N) BrCl solution in Section 7.6 of Method 1631B
to produce the following solutions:
A7.5.1 0.07 N bromine monochloride solution—Dilute 300 mL of 0.2N BrCl solution to 1000
mL with reagent water in a fluoropolymer bottle.
A7.5.2 0.02 N bromine monochloride solution—Dilute 100 mL of concentrated BrCl solution
to 1000 mL with reagent water in a fluoropolymer bottle.
A8.0 Sample Collection, Preservation, and Storage
A8.1 Samples are collected into acid-cleaned glass, polyethylene, or fluoropolymer jars. For all except
very low level and high water content samples, polyethylene bags are also acceptable. Dry solids
5
such as coal and ores may be collected and stored in heavy gauge paper pouches commonly used by
geologists.
A8.2 Samples are collected using clean gloves. Equipment is rinsed between samples to avoid
cross-contamination. In general, follow the sampling procedures in Method 1613B. The ultra-low
level sampling procedures in EPA Method 1669 may not be necessary because Hg concentrations in
solids are typically 103 - 107 times higher than those found in water samples.
A8.3 Sample shipment, storage, preservation, and holding times
A8.3.1 Dry samples—Samples such as ores, coal, paper, and wood may be shipped
unrefrigerated and stored indefinitely in a cool, dry location known to have an
atmosphere that is low in mercury.
A8.3.2 Biota samples—Samples containing biota, including wet and dry sludge, are shipped to
the laboratory at 0-4 EC and may be processed and stored in one of the following two
ways:
A8.3.2.1 Biota samples large enough to sub-sample are homogenized to a fine paste with a
stainless steel mill, or finely chopped with stainless steel tools on an
acid-cleaned, plastic cutting board. After homogenization, samples are stored
frozen at < -15 EC in an acid-cleaned glass or fluoropolymer jar. The jar should
be sized to be filled between 50 - 80% with sample. Samples may be stored
frozen for a maximum of 1 year.
A8.3.2.2 If not analyzed upon receipt at the laboratory, biota samples may be lyophilized
(freeze-dried) prior to homogenization and storage. Once lyophilized, biota
samples may be stored unrefrigerated in a low-mercury atmosphere for a
maximum of 1 year.
A8.3.3 Wet sediment samples—Wet sediment samples are chilled and shipped to the
laboratory at 0-4 EC. Because freezing and thawing may adversely affect homogeneity
by causing clumping and separation of the solids from the liquid, wet sediment samples
must be aliquoted and weighed at the laboratory and prior to freezing if they are not
analyzed upon receipt. Wet sediment samples may be held for 1 year if aliquoted,
weighed, and frozen at < -15 EC. Sediment samples may be lyophilized and stored
unrefrigerated for 1 year in a low-mercury atmosphere if only total Hg will be
determined and no free elemental mercury (Hg0) is expected to be in the samples.
A9.0 Quality Control
A9.1 The quality control (QC) measures in Section 9 of Method 1631B must be followed when analyzing
samples using this Appendix. In addition, this Appendix requires method blanks. Descriptions of the
modifications of the quality control measures in Method 1631B that are required for application to
solid and semi-solid matrices are provided below.
A9.2 Initial demonstration of laboratory capability
6
A9.2.1 Method detection limit (see Section 9.2.1 of Method 1631B)—The laboratory must
achieve an MDL that is less than or equal to the MDL listed in Table A1.
A9.2.2 Initial precision and recovery (IPR; see Section 9.2.2 of Method 1631B)—Analyze four
aliquots of the appropriate reference matrix (see Appendix Section A7.1), each spiked
with 4.0 ng of Hg. This amount will be 8 ng/g for a 0.5 g sample. Calculate the
average percent recovery (X) and the RSD of percent recovery. Compare X and RSD
with the corresponding IPR limits in Table A1. If X and RSD meet the acceptance
criteria, system performance is acceptable and analysis of samples may begin. If,
however, RSD exceeds the precision limit or X is outside the recovery range,
performance of the analytical system is unacceptable. Correct the problem and repeat
the test.
A9.3 Matrix spike/matrix spike duplicate (MS/MSD; see Section 9.3 of Method 1631B)
9.3.1 Spike and analyze 1 out of every 10 samples of the same matrix type, in duplicate, at a
concentration 2 - 5 times the background concentration of Hg in the unspiked sample or at the
concentration in the IPR (Appendix Section A9.2.2), whichever is greater. Calculate the
percent recovery in each aliquot and the RPD between the aliquots. The individual recoveries
and the RPD shall meet the MS/MSD recovery acceptance criteria in Table A1. If either
recovery or the RPD does not meet the acceptance criteria, correct the problem and repeat the
test according to the procedures in Sections 9.3.4 and/or 9.3.5 of Method 1631B.
A9.4 Blanks (see Section 9.4 of Method 1631B)
A9.4.1 Because of the high concentrations of mercury in solid samples, as compared to
aqueous samples, field blanks (Section 9.4.3 of Method 1631B) and sampler check
blanks (Section 9.4.4.2 of Method 1631B) are not required. However, it may be
prudent to collect a sampler check blank the first time that a given set of sampling
equipment is used and whenever it is suspected to be contaminated.
A9.4.2 Method blank—For each batch of 20 samples (Section 9.1.7 of Method 1631B), digest
and analyze a method blank using the most appropriate reference matrix (Appendix
Section A7.1). The laboratory may process a greater number of method blanks, if
desired, and average the results. The method blank must include all sample processing
steps; e.g., homogenization (Appendix Section A8.3.2.1). The concentration of
mercury in the method blank, or the average of multiple method blanks, must meet the
QC acceptance criteria in Table A1; otherwise, the source of contamination must be
eliminated and the batch reanalyzed.
A9.5 Ongoing precision and recovery (OPR; see Section 9.5 of Method 1631B)—The OPR (laboratory
control sample) for solid and semi-solid samples is test of the entire analytical system and includes
all sample processing procedures; e.g., homogenization (Appendix Section A8.3.2.1) and digestion
(Appendix Section A11.1 or A11.2).
A9.5.1 Analyze an aliquot of the appropriate reference matrix (see Appendix Section A7.1),
spiked at the concentration in the IPR (Appendix Section A9.2.2). Calculate the
percent recovery.
7
A9.5.2 Compare percent recovery with the OPR limit in Table A1. If percent recovery meets
the acceptance criteria, system performance is acceptable and analysis of samples and
blanks may continue. If, however, percent recovery is outside of the acceptance range,
analytical system performance is unacceptable. Correct the problem and repeat the test
according to Section 9.5.2 of Method 1631B.
A9.6 Quality Control Sample (QCS) - Many certified reference materials (CRMs) are available for total
mercury in plants, animals, fish, sediments, soils, and sludge. Recovery and precision for at least
one QCS per batch of samples must meet the performance specifications provided by the supplier.
A9.7 Replicate samples—Some samples, particularly sediments, may be heterogeneous. Replicates of
these samples should be analyzed to characterize this heterogeneity. Replicate samples may also be
required by a specific program to assess the precision of the sample collection, transportation, and
storage techniques. The relative percent difference (RPD) between replicates should be less than
30%.
A10.0 Calibration and Standardization
A10.1 Calibrate the CVAFS instrument system using the procedures in Section 10 of Method
1631B. The concentration of the calibration solutions is as given in Section 10.1.1.2 of
Method 1613B. The amount of Hg in these solutions will be 0.05, 0.5, 2.5, 5.0, and
10.0 ng.
A10.2 Calibration verification (VER)—Calibration of the CVAFS instrument system must be
verified periodically using aqueous standards. In Method 1631B, the OPR is used for
this verification because the standards are added to water (see Sections 10.2 and 9.5 of
Method 1631B). In contrast, the OPR in this Appendix (Appendix Section A9.5) is
used to demonstrate that the end-to-end analytical system remains in control. To avoid
confusion, the periodic verification of calibration in this Appendix is referred to as
"calibration verification" (VER). The VER is a spiked reagent water sample (an
aqueous blank spike) and is used to determine that the CVAFS remains in control.
A10.2.1 Prior to and after the analysis of 10 samples, verify calibration of the CVAFS
instrument system using the OPR test in Sections 9.5.1 and 9.5.2 of Method
1631B. Record results as calibration verification (VER).
A10.2.2 The requirements in Section 9.5.2 of Method 1631B must be met for sample
results to be valid.
A11.0 Digestion
A11.1 Digestion I: Hot re-fluxing HNO3/H2SO4 digestion followed by BrCl oxidation—This
procedure is intended for biota, wood, paper, tissue, municipal sludge, and other primarily
organic matrices (excluding coal). It does, however, give quantitative recovery for Hg on
finely divided geological matrices such as sediments and soils.
A11.1.1 Accurately weigh (to the nearest mg) an aliquot of sample directly into a tared digestion
vessel (Appendix Section A6.1). For organic matter such as biota, weigh 0.2-0.4 gram;
for tissue (e.g., fish), plant material, or sludge, weigh 0.5-1.5 grams; for dried material
8
such as wood, paper, and CRMs, weigh 0.2-0.4 gram. The use of too much organic
material will consume all of the acid in the digestion, resulting in a low recovery.
A11.1.2 To each sample, add 10.0 mL of HNO3/H2SO4 solution (Appendix Section A7.4).
Place the digestion vessel in an acid fume hood and loosely cap with a clean marble or
inverted fluoropolymer cone (Appendix Section A6.2). For wood, paper, or other dry
carbohydrates that can react violently with the HNO3/H2SO4 solution, allow the sample
to sit in the cold acid for at least 4 hours before heating.
A11.1.3 After digesting at room temperature, place the digestion vessel on a hot plate in the
hood and slowly bring to a gentle boil by incrementally increasing the plate temperature
over a 1-hour period. If excessive sample foaming occurs, bring to temperature more
slowly. Reflux for 2-3 hours to fully oxidize remaining organic matter. The mineral
portion of soil and sediment samples will not dissolve but will be effectively leached by
this digestion.
A11.1.4 After the digestion is complete, bring to the calibration mark on the digestion vessel (40
± 0.5 mL; Appendix Section A6.1) with 0.02 N BrCl solution (Appendix Section
A7.5.2) and mix thoroughly. Shake the sample/BrCl solution to homogenize, and allow
to sit at least 4 hours prior to analysis to oxidize remaining dissolved methyl Hg.
Analyze the oxidized digestate per Appendix Section A12.0.
Note: Some highly organic matrices will require higher levels of BrCl (Appendix Section
A7.5.1) and longer digestion times or elevated temperatures. The amount of reagent added to
a sample must be the same as the amount added to the reagent blank to detect contamination
in the reagents, and to the method blank and the OPR to demonstrate that mercury can be
recovered quantitatively. BrCl oxidation must be continued until it is complete.
A11.2 Digestion II: Cold aqua regia followed by BrCl oxidation—This procedure is intended for
coal, ores, sediments, soils, and other geological media. It does, however, give quantitative
recovery for Hg on finely divided biological media such as tissues, paper, and wood, because
the organic matrix is leached rather than dissolved. Solid, dry geological media such as rocks,
ores, and coal must be pulverized using a contamination-free mill prior to digestion.
Otherwise, mercury will not be recovered from the interior of large particles.
A11.2.1 Accurately weigh (to the nearest mg) an aliquot of the sample directly into a tared
digestion vessel. For wet sediments and soils, weigh 0.5-1.5 grams; for dried materials
such as coal, ores, and CRMs, weigh 0.5-1.0 gram. To better assure homogeneity,
sediments and soils should be screened through a 2-mm plastic sieve to remove large
rocks and sticks before digestion.
A11.2.2 In a fume hood, add 8.0 mL of concentrated HCl (Method 1631B Section 7.3), swirl,
and add 2.0 mL of concentrated HNO3 to the sample in the digestion vessel. Cap the
vessel with a clean glass marble or inverted fluoropolymer cone. Allow to digest at
room temperature for at least 4 hours but preferably overnight.
A11.2.3 For coal or other elemental carbon-containing sample, dilute the digestate to the
calibration mark (40 ± 0.5 mL) with 0.07 N BrCl solution and shake the flask to mix
thoroughly. The addition of BrCl ensures that Hg will not re-adsorb to the carbon
9
particles, producing low recoveries. After dilution and shaking, allow the sample to
settle overnight, or centrifuge prior to analysis. Be sure that all fine-grained particles
are completely settled prior to analysis. This settling can be hastened by centrifuging
for 20 minutes at 3000 RPM or by filtering the sample through a 0.45-mm filter.
Analyze per Appendix Section A12.0.
A11.2.4 For other than coal or elemental carbon-containing samples, dilute the digestate to
volume (40 ± 0.5 mL) with reagent water so that the meniscus is at the calibration line
in the neck of the digestion vessel. Shake vigorously and allow settling until the
supernatant is clear prior to analysis. Analyze per Appendix Section A12.0.
A11.3 The diluted digestates may be stored up to one year in glass or fluoropolymer containers prior
to analysis, or for future re-analysis, if needed.
A12.0 Digestate Analysis
Diluted digestates are analyzed in a manner analogous to the analysis of standards by Method 1631B
(see Section 10.0 of Method 1631B).
A12.1 Pipet a 0.01- to 5.0-mL volume of diluted digestate (Appendix Section A11.1.4, A11.2.3, or
A11.2.4) directly into a bubbler containing approximately 100 mL of pre-purged SnCl2-
containing water.
Note: The volume of SnCl2-containing water in the bubbler is not critical for the purpose of purging
but is assumed to be 0.100 L for the purpose of calculating results (see Appendix Section A13.1.1).
A12.2 Purge the solution onto a gold trap for 20 minutes. These conditions allow measurement of
Hg concentrations in the range of 1 – 5,000 ng/g (parts per billion).
A12.3 Change the SnCl2-containing water in the bubbler after a total of 10 mL of digestate has been
added. For example, if 2 digestate aliquots of 5 mL each have been added to 100 mL of fresh,
pre-purged, SnCl2-containing water, the SnCl2-containing water must be changed and 100 mL
of fresh, SnCl2-containing water must be placed in the bubbler and purged for a minimum of
10 minutes prior to addition of another digestate aliquot.
A12.4 For samples known or expected to contain high Hg concentrations, further dilute (usually by a
factor of 100) an aliquot of the diluted digestate with 0.02 N BrCl solution, and analyze a
sub-aliquot.
A13.0 Data Analysis and Calculations
A13.1 Calculation of solid phase concentrations
A13.1.1 The analytical system in Method 1631B will give analytical results in units of area (or
height) for the volume of diluted digestate analyzed. To calculate the solid phase
concentration, use the following equation:
10
CHg = (As - ABB) × V × d × 0.1 / (CFm × v × w)
where:
CHg =concentration of mercury in the sample (ng/g wet weight)
As =peak area (or height) for mercury in the sample
ABB =peak area (or height) for the average of the bubbler blanks
V =volume of diluted digestate (mL) (Appendix Sections A11.1.4, A11.2.3,
A11.2.4) = 40 mL
d =dilution factor(s); e.g., a factor of 100 in Appendix Section A12.4.
0.1 =volume in bubbler (L) (Assumed per note in Appendix Section A12.1)
CFm =mean CF from calibration (area (or height))/(ng/L) (Method 1613B
Section 10.1.1.4)
v =digestate volume analyzed (mL) (Appendix Section A12.1)
w =sample weight (g) (Appendix Section A11.1.1 or A11.2.1)
A13.1.2 If desired, determine the moisture content of a sample aliquot and use the dry weight as
“w” in the equation above.
A13.2 Reporting
A13.2.1 Report results as required in Method 1631B except use reporting levels and units
appropriate to solid samples (ng/g).
A13.2.2 Reagent blank results and method blank results are reported separately and, if
requested or required, are subtracted from sample Hg concentrations.
A14.0 Method Performance
A14.1 This Appendix was developed in a single laboratory and validated in a single laboratory.
Performance data from these studies are summarized in Tables A2 through A7.
A15.0 References
1.Development of Digestion Procedures for Determination of Mercury in Solid and Semi-solid
Samples, Frontier Geosciences, available from EPA Sample Control Center DynCorp I&ET,
Alexandria, VA 22304 (703-461-2100; SCC@dyncorp.com).
2.Single Laboratory Validation of Appendix to Method 1631, June-July 1999, Brooks-Rand Ltd.,
EPA Sample Control Center Episode Number 6236, DynCorp I&ET, Alexandria, VA 22304 (703-
461-2100; SCC@dyncorp.com).
11
Table A1. Quality control acceptance criteria.
Test Acceptance Criteria Spike concentration
Calibration linearity <15% RSD of CF 0.5, 5, 25, 50, and 100 ng/L =
0.05, 0.5, 2.5, 5.0, and 10.0 ng
Calibration verification (VER)77-123%5 ng/L = 0.5 ng
MDL 0.48 ng/g(1)0.8 ng/g
ML 1 ng/g(2)0.05 ng (lowest calibration point)
MS/MSD recovery 70-130%2x background or level in
IPR/OPR, whichever is greater
MS/MSD precision < 30% RPD 2x background or level in
IPR/OPR, whichever is greater
IPR recovery 75-125%4.0 ng
IPR precision < 20% RSD 4.0 ng
OPR recovery 70 - 130%4.0 ng
Method blank < 0.4 ng or < 0.1x sample,
whichever is greater
-
(1) See Appendix Table A4
(2) Assuming a 0.5 g sample
Table A2. Method performance for biological samples and CRMs digested using hot re-fluxing HNO3
digestion plus BrCl dilution and Method 1631B. Blanks and spikes were on three different instruments,
over a period of several weeks. Data provided by Frontier Geosciences.
Hg concentration (ng/g; ppb)
Test/material n mean SD certified(1)Performance
Method blanks 24 0.25 0.13 --DL = 0.33 ng/g(2)
2.0 ng/g matrix spike 28 1.90(3)0.22 2.00 95% rec.; 11% RSD
IRM-007 (sludge)3 3,680 150 3,150 117% rec.; 4% RSD
DOLT-2 (fish liver)7 2,164 161 2,140 101% rec.; 7%RSD
DORM-2 (fish muscle)11 4,682 386 4,640 101% rec.; 8% RSD
NIST-2796 (mussel)12 60.4 6.7 61.0 99% rec.; 11% RSD
(1) value provided by supplier of reference material
(2) detection limit = 2.5 x SD for 24 method blanks (2.5 = student's t @ 23 degrees of freedom)
(3) net recovered; background concentration (chicken breast) was 0.41 ng/g
12
Table A3. Method performance for geological samples and CRMs using cold aqua regia digestion and
Method 1631B. Data provided by Frontier Geosciences.
Hg concentration (ng/g; ppb)
Test/material n mean SD certified(1)Performance
Method blanks 23 0.045 0.037 --DL = 0.09 ng/g(2)
0.5 ng/g blank spike 8 0.465 0.079 0.50 MDL = 0.24 ng/g
NIST-2709 (soil)9 1393 111 1,400 100% rec.; 8% RSD
NIST-1633 (fly ash)2 163 3.0 160 102% rec.; 2% RSD
NIST-2710 (soil)3 30888 2,692 32,610 95% rec.; 9% RSD
IAEA-356 (sediment)1 7152 --7.62 94% rec.
PACS-1 (sediment)1 4402 --4,540 97% rec.
NIST-1630 (coal)3 108 5.0 127*85% rec.; 5% RSD
NIST-1632 (coal)5 79.3 7.0 78 102% rec.; 9% RSD
(1) value provided by supplier of reference material
(2) detection limit = 2.5 x SD for 24 method blanks (2.5 = student's t @ 23 degrees of freedom)
Table A4. Results of MDL Set 2 analyses (spiked with 0.24 ng; ~0.8 ng/g). Data provided by Brooks-
Rand.
Rep Sample
Mass (g)
Measured Hg (ng)Blank-corrected Hg
(ng)
Sample Concentration
(ng/g)*
1 1.03 0.39 0.13 0.41
2 1.29 0.50 0.23 0.71
3 1.25 0.48 0.22 0.73
4 1.36 0.53 0.26 0.78
5 1.28 0.49 0.23 0.68
6 1.01 0.39 0.12 0.40
7 1.17 0.45 0.19 0.61
*blank corrected Average: 0.62 ng/g
Std. Dev.: 0.15 ng/g
MDL = 0.48
13
Table A5. Analyses of spiked catfish samples (spiked with 17 ng of Hg). Data provided by Brooks-Rand
Replicate Sample Mass (g)Measured Hg
(ng)
Recovered Hg
(ng)*
%Recovery*
1 1.02 30.1 17.1 99.3
2 1.21 31.6 16.2 93.7
3 0.97 31.4 19.0 110.2
4 1.17 23.4 8.41 48.7
*background corrected Average: 88%
Std. Dev.: 27%
Table A6. Analyses of spiked powdered egg yolk (spiked with 2.9 ng of Hg). Data provided by Brooks-
Rand.
Replicate Sample Mass (g)Measured Hg
(ng)
Recovered Hg*
(ng)
%Recovery
1 1.00 3.49 2.34 80.6
2 1.06 3.16 1.94 67
3 1.04 2.56 1.37 47.1
4 1.08 3.75 2.50 86.2
*background corrected Average: 70%
Std. Dev.: 17%