United States
Environmental Protection
Agency
Office of Water
Engineering and Analysis Division (4303)
Washington, DC 20460
EPA-821-B-94-004
October 1994
vvEPA Method 1664:
N-Hexane Extractable Material (HEM)
and Silica Gel Treated N-Hexane
Extractable Material (SGT-HEM)
by Extraction and Gravimetry
(Oil and Grease and Total Petroleum
Hydrocarbons) >
Printed on FtocyctBd Paper
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United States Office of Water EPA-821-B-94-004
Environmental Protection Engineering and Analysis Division (4303) October 1994
Agency Washington, DC 20460
&EPA Method 1664:
N-Hexane Extractable Material (HEM)
and Silica Gel Treated N-Hexane
Extractable Material (SGT-HEM)
by Extraction and Gravimetry
(Oil and Grease and Total Petroleum
Hydrocarbons)
) Printed on Recycled Pat
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Acknowledgments
This method was prepared under the direction of William A. Telliard of the
Engineering and Analysis Division within the EPA Office of Water.
This document was prepared under EPA Contract No. 68-C3-0337 by the
Environmental Services Division of DynCorp Viar, Inc.
Disclaimer
This method has been reviewed by the Engineering and Analysis Division,
U.S. Environmental Protection Agency, and approved for publication.
Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.
I,
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Method 1664
Introduction
As a party to the Montreal Protocol on Substances that Deplete the Ozone Layer and as required by
law under the Clean Air Act Amendments of 1990 (CAAA), the United States is committed to
controlling and eventually phasing out the use of chlorofluorocarbons (CFCs). In support of these
efforts, Method 1664 was developed by the United States Environmental Protection Agency Office of
Science and Technology to replace previously used gravimetric procedures that employed Freon- 113, a
Class I CFC, as the extraction solvent for the determination of oil and grease and petroleum hydrocar-
bons.
Method 1664 is a performance based method applicable to aqueous matrices that requires the use of n-
hexane as the extraction solvent and gravimetry as the determinative technique. Alternative extraction
and concentration techniques are allowed, provided that all performance specifications are met. In
addition, QC procedures designed to monitor precision and accuracy have been incorporated into
Method 1664.
Questions concerning this method or its application should be addressed to:
W.A. Telliard
USEPA Office of Water
Analytical Methods Staff
Mail Code 4303
401 M Street, SW
Washington, D.C. 20460
202/260-7120
Requests for additional copies should be directed to:
Water Resource Center
Mail Code RC-4100
401 M Street, SW
Washington, D.C. 20460
202/260-7786 or 202/260-2814
II,
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Method 1664
N-Hexane Extractable Material (HEM) and Silica Gel Treated N-
Hexane Extractable Material (SGT-HEM) by Extraction and Gravimetry
(Oil and Grease and Total Petroleum Hydrocarbons)
1.0 Scope and Application
1.1 This method is for the determination of n-hexane extractable material (HEM) and n-hexane
extractable material that is not adsorbed by silica gel (SGT-HEM) in surface and saline waters
and industrial and domestic aqueous wastes. Extractable materials that may be determined are
relatively non-volatile hydrocarbons, vegetable oils, animal fats, waxes, soaps, greases, and
related materials.
1.2 This method is for use in the Environmental Protection Agency’s (EPA’ s) survey and monitoring
programs under the Federal Water Pollution Control Act and Amendments. ‘Oil and grease’ is a
conventional pollutant defmed in the Act and codified at 40 CFR 401.16. The term “n-hexane
extractable material” reflects that this method can be applied to materials other than oils and
greases. Similarly, the term “silica gel treated n-hexane extractable material” reflects that this
method can be applied to materials other than aliphatic petroleum hydrocarbons that are not
adsorbed by silica gel.
1.3 This method is not applicable to measurement of materials that volatilize at temperatures below
approximately 85°C. Petroleum fuels from gasoline through #2 fuel oil may be partially lost in
the solvent removal operation.
1.4 Some crude oils and heavy fuel oils contain a significant percentage of materials that are not
soluble in n-hexane. Accordingly, recoveries of these materials may be low.
1.5 This method is capable of measuring HEM in the range of 2 to 1000 mgIL and SGT-HEM in the
range of 5 to 1000 mgfL, and may be extended to higher levels by analysis of a smaller sample
volume collected separately.
1.6 For this method, the Method Detection Limit (MDL; 40 CFR 136, Appendix B) has been
determined as 0.91 mgfL for HEM and 1.6 mgIL for SGT-HEM (Reference 16.1), and the
Minimum Level (ML; Reference 16.3) has been set at 2.0 mg/L for HEM and 5.0 mg/L for
SGT-HEM (Reference 16.1).
1.7 This method is “performance-based”. The analyst is permitted to modify the method to over-
come interferences or lower the cost of measurements, provided that all performance criteria in
this method are met. The requirements for establishing method equivalency are given in Section
9.1.2.
1.8 Any modification of this method, beyond those expressly permitted, shall be considered a major
modification subject to application and approval of alternate test procedures under 40 CFR 136.4
and 136.5.
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Method 1664
1.9 Each laboratory that uses this method must demonstrate the ability to generate acceptable results
using the procedure in Section 9.2.
2.0 Summary of Method
2.1 A I -L sample is acidified to pH <2 and serially extracted three times with n-hexane in a
separatory funnel. The extract is dried over sodium sulfate.
2.2 The solvent is evaporated from the extract and the HEM is weighed. If the HEM is to be used
for determination of SGT-HEM, the HEM is redissolved in n-hexane.
2.3 For SGT-HEM determination, an amount of silica gel proportionate to the amount of HEM is
added to the solution containing the redissolved HEM to remove adsorbable materials. The
solution is filtered to remove the silica gel, the solvent is evaporated, and the SGT-HEM is
weighed.
2.4 Quality is assured through calibration and testing of the extraction, concentration, and gravimet-
nc systems.
3.0 Definitions
3.1 HEM and SGT-HEM are method-defined analytes; i.e., the defmitions of both HEM and SGT-
HEM are dependent on the procedure used. The nature of the oils and/or greases, and the
presence of extractable non-oily matter in the sample will influence the material measured and
interpretation of results.
3.2 Definitions for terms used in this method are given in the glossary at the end of the method.
4.0 Interferences
4.1 Solvents, reagents, glassware, and other sample-processing hardware may yield artifacts that
affect results. Specific selection of reagents and purification of solvents may be required.
4.2 All materials used in the analysis shall be demonstrated to be free from interferences under the
conditions of analysis by running laboratory blanks as described in Section 9.4.
4.3 Glassware is cleaned by washing in hot water containing detergent, rinsing with tap and distilled
water, and rinsing with solvent or baking. Boiling flasks that will contain the extracted residue
are dried in an oven at 105—115°C and stored in a desiccator.
4.4 Sodium sulfate and silica gel fmes have the potential to inflate results for HEM and SGT-HEM
by passing through the filter paper. If the filter paper specified in this method is inadequate for
removal of these fines, use of a 0.45-micron filter is recommended.
4.5 Interferences extracted from samples will vary considerably from source to source, depending
upon the diversity of the site being sampled. For those instances in which samples are thought
to consist of complex matrices containing substances (such as particulates or detergents) that may
interfere with the extraction procedure, a smaller sample may need to be collected for analysis.
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Method 1664
5.0 Safety
5.1 The toxicity or carcinogenicity of each reagent used in this method has not been precisely
determined; however, each chemical should be treated as a potential health hazard. Exposure to
these chemicals should be reduced to the lowest possible level.
5.2 n-Hexane has been shown to have increased neurotoxic effects over other hexanes and some
other solvents. Inhalation of n-hexane should be minimized by performing all operations with n-
hexane in a hood or well-ventilated area.
5.3 Unknown samples may contain high concentrations of volatile toxic compounds. Sample
containers should be opened in a hood and handled with gloves to prevent exposure.
5.4 This method does not address all safety issues associated with its use. The laboratory is respon-
sible for maintaining a safe work environment and a current awareness file of OSHA regulations
regarding the safe handling of the chemicals specified in this method. A reference file of
material safety data sheets (MSDSs) should be made available to all personnel involved in these
analyses. Additional information on laboratory safety can be found in References 16.4—16.6.
6.0 Equipment and Supplies
Note: Brand names, suppliers, and part numbers are for illustrative purposes only. No
endorsement is implied. Equivalent performance may be achieved using apparatus and materials
other than those specified here, but demonstration of equivalent performance that meets the
requirements of this method is the responsibility of the laboratory.
6.1 Sampling equipment.
6.1.1 Sample collection bottles: Glass, approximately 1 L, with PTFE-lined screw cap.
Note: In those instances necessitating collection of a smaller aliquot, a smaller sample
container nay be used.
6.1.2 Cleaning.
6.1.2.1 Bottles: Detergent water wash, tap water rinse, cap with aluminum foil, and bake
at 200—250°C for 1 h minimum prior to use. Solvent rinse may be used in place
of baking.
6.1.2.2 Liners for screw caps: Detergent water wash, tap water and solvent rinse, and
bake at 110—200°C for I h minimum prior to use.
6.1.3 Bottles and liners must be lot-certified to be free of artifacts by running laboratory blanks
according to this method (per Section 9.4). If blanks from bottles and/or liners without
cleaning or with fewer cleaning steps than required above show no detectable materials,
the bottle and liner cleaning steps that do not eliminate these artifacts may be omitted.
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Method 1664
6.2 Equipment for glassware cleaning.
6.2.1 Laboratory sink with overhead fume hood.
6.2.2 Oven: Capable of maintaining a temperature within ± 5°C in the range of 100—250°C.
6.3 Equipment for calibration.
6.3.1 Analytical Balance: Capable of weighing 0.1 mg.
6.3.2 Volumetric flask: 100-mL glass.
6.3.3 Vials: Assorted sizes, with PTFE-lined screw caps.
6.3.4 Volumetric pipette: 5-mL glass.
6.4 Equipment for sample extraction.
6.4.1 Balance: Top loading, capable of weighing 500—2000 g within ± 1%.
6.4.2 Glass stirring rod.
6.4.3 Separatory funnel: 2000-mL, with PTFE stopcock.
6.4.4 Funnel: Large, glass, for pouring sample into separatory funnel.
6.4.5 Centrifuge: Capable of spinning at least four lOO-mL glass centrifuge tubes at 2400 rpm
minimum.
6.4.6 Centrifuge tubes: 100-mL glass.
6.5 Equipment for removal of water, sodium sulfate, and silica gel fines.
6.5.1 Funnel: Analytical, glass.
6.5.2 Filter paper: Whatman No. 40 (or equivalent), to fit funnel.
6.6 Equipment for solvent evaporation.
6.6.1 Water bath: Capable of maintaining a temperature of approximately 85°C.
6.6.2 Flask: Boiling, 125-mL (Corning No. 4100 or equivalent).
6.6.3 Distilling head: Claisen (VWR Scientific No. 26339-005, or equivalent), includes Clai-
sen-type connecting tube and condenser.
6.6.4 Distilling adaptor (attached to the distilling head and to the waste collection flask for
recovery of solvent).
6.6.5 Waste collection flask (attached to the distilling adaptor for collection of the distilled
solvent).
6.6.6 Ice bath (to aid in the condensation and collection of the distilled solvent).
6.6.7 Vacuum, pump or other source of vacuum.
6.6.8 Desiccator: Cabinet- or jar-type, capable of keeping the boiling flask (Section 6.6.2) dry
during cooling.
6.7 Equipment for removal of adsorbable materials.
6.7.1 Magnetic stirrer.
6.7.2 PTFE-coated magnetic stirring bars.
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Method 1664
6.7.3 Graduated cylinder: 500-mL, capable of measuring ± 5 mL.
6.7.4 Pipettes: Assorted sizes, calibrated to within ± 0.5 percent.
7.0 Reagents and Standards
Note: Brand names, suppliers, and part numbers are for illustrative purposes only. No
endorsement is implied. Equivalent performance may be achieved using apparatus and materials
other than those specified here, but demonstration of equivalent performance meeting require-
ments of this method is the responsibility of the laboratory.
7.1 Reagent water: Water in which HEM is not detected at or above the Minimum Level of this
method. Bottled distilled water, or water prepared by passage of tap water through activated
carbon have been shown to be acceptable sources of reagent water.
7.2 Hydrochloric or sulfuric acid: ACS, 1:1. Mix equal volumes of cone. HC1 or H 1 S0 4 and
reagent water.
7.3 n-Hexane: 85% purity, 99.0% mm. saturated C 6 isomers, residue less than 1 mgIL.
7.4 Acetone: ACS, residue less than 1 mgIL.
7.5 Sodium sulfate: ACS, granular anhydrous.
Note: Powdered sodium sulfate should not be used because traces of water will cause it to
solidify.
7.6 Boiling chips: Silicon carbide or PTFE.
7.7 Silica gel: Anhydrous, 60 - 200 mesh (Davidson Grade 950 or equivalent). Dry at 200—250°C
for 24 h minimum and store in a desiccator or tightly sealed container. Determine the n-hexane
soluble material content of the silica gel by extracting 30 g of silica gel with n-hexane and
evaporating the n-hexane to dryness. The silica gel must contain less than 5 mg of n-hexane
soluble material per 30 g (<0.17 mg/g).
7.8 Hexadecane: 98% minimum purity.
7.9 Stearic acid: 98% minimum purity.
7.10 Hexadecane/stearic acid (1:1) spiking solution: Prepare in acetone at a concentration of 4
mg/niL each.
7.10.1 Place 400 ± 4 mg stearic acid and 400 ± 4 mg hexadecane in a 100-niL volumetric flask
and fill to the mark with acetone.
Note: The solution may require warming for complete dissolution of stearic acid.
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Method 1664
7.10.2
After the hexadecane and
mL vial with PTFE-lined
stearic acid have dissolved, transfer the
cap. Mark the solution level on the vial
solution to a
and store in
100—150
the dark
at room temperature.
7.10.3
Immediately prior to use, verify the level on the vial and bring to
if required. Warm to redissolve all visible precipitate.
volume with
acetone,
Note: If there is doubt of the concentration, remove 5.00 ± 0.05 mL with a volumetric pipet,
place in a tared weighing pan, and evaporate to d,yness in a fume hood. The weight must be 40
± I mg.
7.11 Precision and recovery (PAR) standard: Spike 5.00 ± 0.05 mL of the hexadecane/stearic acid
spiking solution (Section 7.10) into 950—1050 mL of reagent water to produce concentrations of
approximately 20 mgIL each of hexadecane and stearic acid. The PAR standard is used for the
determination of initial precision and recovery (Section 9.2.2) and ongoing precision and recov-
ery (Section 9.6).
7.12 The spiking solutions should be checked frequently for signs of degradation or evaporation and
must be replaced after six months, or sooner if degradation has occurred.
8.0 Sample Collection, Preservation, and Storage
8.1 Collect approximately one liter of representative sample in a glass bottle following conventional
sampling practices (Reference 16.7), except that the bottle must not be pre-nnsed with sample
before collection.
8.1.1 If analysis is to be delayed for more than a few hours, preserve the sample by adding 5
niL of HCI or H 2 S0 4 solution (Section 7.2) at the time of collection, and refrigerate at
0 -4°C (40 CFR 136, Table II).
8.1.2 If a sample is known or suspected to contain greater than 1000 mgfL of extractable
material, collect a proportionately smaller volume of sample (the volume required will
depend upon the estimated amount of extractable material) in a glass bottle. Add a
proportionately smaller amount of HC1 or H 2 S0 4 solution to the smaller sample if preser-
vation is necessary.
8.2 Collect an additional two aliquots (1 L, additional smaller volume, or both) of a sample for each
set of ten samples or less for the matrix spike and matrix spike duplicate.
Note: For those circumstances requiring the collection of multiple aliquots of one sample,
each aliquot is to be collected in either of the following ways: 1) collect the total volume
needed in one container, homogenize by mixing with a stir bar until a vortex forms, and transfer
to required aliquots, 2) collect simultaneously in parallel, jf possible, or 3) collect as grab
samples in rapid succession.
8.3 The high probability that extractable matter may adhere to sampling equipment and result in
measurements that are biased low precludes the collection of composite samples for determina-
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Method 1664
tion of oil and grease. Therefore, samples must be collected as grab samples. If a composite
measurement is required, individual grab samples collected at prescribed time intervals must be
analyzed separately and the concentrations averaged.
8.4 All samples must be refrigerated at 0—4°C from the time of collection until extraction (40 CFR
136, Table II).
8.5 All samples must be analyzed within 28 days of the date and time of collection (40 CFR 136,
Table II).
9.0 Quality Control
9.1 Each laboratory that uses this method is required to operate a formal quality assurance program
(Reference 16.8). The minimum requirements of this program consist of an initial demonstration
of laboratory capability, ongoing analyses of standards and blanks as a test of continued perfor-
mance, and analyses of matrix spike (MS) and matrix spike duplicate (MSD) samples to assess
accuracy and precision. Laboratory performance is compared to established performance criteria
to determine if the results of analyses meet the performance characteristics of the method.
9.1.1 The analyst shall make an initial demonstration of the ability to generate acceptable
accuracy and precision with this method. This ability is established as described in
Section 9.2.
9.1.2 In recognition of advances that are occurring in analytical technology, the analyst is
permitted certain options to improve separations or lower the costs of measurements,
provided that all performance specifications are met. These options include alternate
extraction and concentration devices and procedures such as solid-phase extraction and
Kuderna-Danish concentration. Alternate determinative techniques, such as infra-red
spectroscopy or immuno-assay, and changes that degrade method performance, are not
allowed. If an analytical technique other than the techniques specified in this method is
used, that technique must have a specificity equal to or better than the specificity of the
techniques in this method for HEM and/or SGT-HEM in the sample of interest.
9.1.2.1 Each time a modification is made to this method, the analyst is required to repeat
the IPR test in Section 9.2.2 to demonstrate that the modification produces results
equivalent to or better than results produced by this method. If the detection
limit of the method will be affected by the modification, the analyst must demon-
strate that the MDL (40 CFR 136, Appendix B) is less than or equal to the MDL
in this method or one-third the regulatory compliance level, whichever is higher.
If the modified method is to be used for compliance monitoring, the discharger
must also demonstrate that the modified method recovers at least as much HEM
and/or SOT-HEM as this method on each specific discharge. The tests required
for this equivalency demonstration are given in Sections 9.1.2.1.1-9.1.2.1.3.
9.1.2.1.1 Collect, extract, concentrate, and weigh the HEM or SGT-HEM in two
sets of four aliquots of unspiked wastewater. One set of four waste-
water aliquots is analyzed according to the protocol in Section 11 of
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Method 1664
this method and the other set of four aliquots is analyzed using the
modified method.
9.1.2.1.2 Compute the average percent recovery of HEM and SGT-HEM for the
set of results from this method and for the set of results from the modi-
fied method. The average percent recovery using the modified method
must be equal to or greater than 79 percent of the average percent
recovery produced by this method for HEM and 66 percent of the
average percent recovery produced by this method for SGT-HEM. If
not, the modified method may not be used.
Note: if the average concentration of the four results produced using this method is below the
Minimum Level (Section 1.6), proceed as follows:
9.1.2.1.3 Extract and concentrate a sufficient amount of wastewater to produce a
minimum of 160 mg of HEM or SGT-HEM. Dissolve this material in
acetone and spike 20 - 50 mg of the material into each of eight aliquots
of wastewater. Use these eight aliquots for the equivalency test (Sec-
tions 9.1.2.1.1-9.1.2.1.2).
Note: if more than 10 liters of wastewater must be extracted to produce 160 mg of HEM or
SGT-HEM, and if the equivalency test of the modified method is passed for spikes of reference
standards into reagent waster (Section 9.2.2), the mod fied method is deemed to be equivalent to
this method for determining HEM and or SGT-HEM on that specific discharge.
9.1.2.2 The laboratory is required to maintain records of modifications made to this
method. These records include the following, at a minimum:
9.1.2.2.1 The names, titles, addresses, and telephone numbers of the analyst(s)
who performed the analyses and modification, and of the quality control
officer who witnessed and will verify the analyses and modification.
9.1.2.2.2 A listing of pollutant(s) measured (HEM and/or SOT-hEM).
9.1.2.2.3 A narrative stating reason(s) for the modification.
9.1.2.2.4 Results from all quality control (QC) tests comparing the modified
method to this method, including:
(a) Calibration (Section 10).
(b) Calibration verification (Section 9.5).
(c) Initial precision and recovery (Section 9.2.2).
(d) Analysis of blanks (Section 9.4).
(e) Accuracy assessment (Section 9.3).
(I) Ongoing precision and recovery (Section 9.6).
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Method 1664
9.1.2.2.5 Data that will allow an independent reviewer to validate each deter-
mination by tracing the instrument output (weight or other signal) to the
final result. These data are to include:
(a) Sample numbers and other identifiers.
(b) Extraction dates.
(c) Analysis dates and times.
(d) Analysis sequence/run chronology.
(e) Sample weight or volume (Section 11.1.4).
(f) Extract volume for SGT-l-IEM (Section 11.5.2).
(g) Make and model of analytical balance and weights traceable to
NIST.
(h) Copies of logbooks, printer tapes, and other recordings of raw data.
(i) Data system outputs, and other data to link the raw data to the
results reported.
9.1.3 Analyses of matrix spike and matrix spike duplicate samples are required to demonstrate
method accuracy and precision and to monitor matrix interferences (interferences caused
by the sample matrix). The procedure and QC criteria for spiking are described in
Section 9.3.
9.1.4 Analyses of laboratory blanks are required to demonstrate freedom from contamination.
The procedure and criteria for analysis of a blank are described in Section 9.4.
9.1.5 The laboratory shall, on an ongoing basis, demonstrate through calibration verification
and analysis of the ongoing precision and recovery sample that the analysis system is in
control. These procedures are described in Sections 9.5 and 9.6, respectively.
9.1.6 The laboratory should maintain records to defme the quality of data that is generated.
Development of accuracy statements is described in Sections 9.3.7 and 9.6.3.
9.1.7 Accompanying QC for the determination of HEM and/or SGT-HEM is required per
analytical batch. An analytical batch is a set of samples extracted at the same time, to a
maximum of 10 samples. Each analytical batch of 10 or fewer samples must be accom-
panied by a laboratory blank (Section 9.4), an ongoing precision and recovery sample
(OPR, Section 9.6), and a matrix spike and matrix spike duplicate (MSIMSD, Section
9.3), resulting in a minimum of five analyses (1 sample, 1 blank, 1 OPR, I MS, and I
MSD) and a maximum of 14 analyses (10 samples, I blank, 1 OPR, 1 MS, and 1 MSD)
in the batch. If greater than 10 samples are to be extracted at one time, the samples must
be separated into analytical batches of 10 or fewer samples.
9.2 Initial demonstration of laboratory capability.
9.2.1 Method Detection Limit (MDL)—To establish the ability to detect HEM and SGT-HEM,
the analyst shall determine the MDL per the procedure in 40 CFR 136, Appendix B
using the apparatus, reagents, and standards that will be used in the practice of this
method. An MDL less than or equal to the MDL in Section 1.6 must be achieved prior
to the practice of this method.
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Method 1664
9.2.2 Initial precision and recovery (IPR)—To establish the ability to generate acceptable
precision and accuracy, the analyst shall perform the following operations:
9.2.2.1 Extract and evaporate four samples of the PAR standard (Section 7.11) according
to the procedure beginning in Section 11.
9.2.2.2 Using the results of the set of four analyses, compute the average percent recov-
ery (X) and the standard deviation of the percent recovery (s) for HEM and for
SGT-HEM (if determined). Use the following equation for calculation of the
standard deviation of the percent recovery:
Equation 1
s__ j _ ifl
where:
n = Number of samples
x = Concentration in each sample
9.2.2.3 Compare s and X with the corresponding limits for initial precision and recovery
in Table 1. If s and X meet the acceptance criteria, system performance is ac-
ceptable and analysis of samples may begin. If, however, s exceeds the precision
limit or X falls outside the range for recovery, system performance is unaccept-
able. In this event correct the problem, and repeat the test.
9.3 Matrix spikes—The laboratory must spike, in duplicate, a minimum of 10 percent of all samples
(one sample in each batch of ten samples) from a given sampling site. The two sample aliquots
shall be spiked with the hexadecane/stearic acid spiking solution (Section 7.10).
9.3.1 The concentration of the spike in the sample shall be determined as follows:
9.3.1.1 If, as in compliance monitoring, the concentration of HEM or SGT-FIEM in the
sample is being checked against a regulatory concentration limit, the spiking level
shall be at that limit or at I to 5 times higher than the background concentration
of the sample (determined in Section 9.3.2), whichever concentration is higher.
9.3.1.2 If the concentration of HEM or SGT-HEM in a sample is not being checked
against a limit, the spike shall be at the concentration of the precision and recov-
ery standard (Section 7.11) or at 1 to 5 times higher than the background concen-
tration, whichever concentration is higher.
9.3.2 Analyze one sample aliquot out of each set of ten samples from each site according to
the procedure beginning in Section 11 to determine the background concentration (B) of
HEM or SGT-I-IEM.
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Method 1664
9.3.2.1 If necessary, prepare a standard solution appropriate to produce a level in the
sample at the regulatory compliance limit or at 1 to 5 times the background
concentration (per Section 9.3.1).
9.3.2.2 Spike two additional sample aliquots with the spiking solution and analyze these
aliquots to determine the concentration after spiking (A).
9.3.3 Calculate the percent recovery (P) of HEM or SGT-HEM in each aliquot using the
following equation:
Equation 2
= 100 (A - B)
T
where:
A = Measured concentration of analyte after spiking
B = Measured background concentration of HEM or SGT-HEM
T True concentration of the spike (40 mg/L)
When determining SGT-HEM, the true concentration (T) must be divided by 2 to reflect
the concentration of hexadecane that remains after removal of stearic acid (20 mg/L).
9.3.4
Compare the percent recovery of the HEM or SGT-HEM with the corresponding QC
acceptance criteria in Table 1.
9.3.4.1 If the results of the spike fail the acceptance criteria, and the recovery of the QC
standard in the ongoing precision and recovery test (Section 9.6) for the analyti-
cal batch is within the acceptance criteria in Table 1, an interference is present.
In this case, the result may not be reported for regulatory compliance purposes.
9.3.4.2 If the results of both the spike and the ongoing precision and recovery test fail
the acceptance criteria, the analytical system is judged to be out of control, and
the problem shall be identified and corrected, and the sample reanalyzed.
9.3.5
Compute the relative percent difference (RPD) between the two results (not between the
two recoveries) using the following equation:
Equation 3
I D 1 -D 2
RPD= ______ xlOO
(D 1 +
where:
D 1 = Concentration of HEM or SGT-HEM in the sample
= Concentration of HEM or SGT—HEM in the second (duplicate) sample
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Method 1664
9.3.6 The relative percent difference for duplicates shall meet the acceptance criteria in Table
1. If the criteria are not met, the analytical system is judged to be out of control, and the
problem must be immediately identified and corrected, and the analytical batch reana-
lyzed.
9.3.7 As part of the QC program for the laboratory, method precision and accuracy for samples
should be assessed and records should be maintained. After the analysis of five spiked
samples in which the recovery passes the test in Section 9.3.4, compute the average
percent recovery (ga) and the standard deviation of the percent recovery (se). Express the
accuracy assessment as a percent recovery interval from a — 2s to a + 2s . For exam-
ple, if a = 90% and s , = 10% for five analyses of HEM or SGT-HEM, the accuracy
interval is expressed as 70—110%. Update the accuracy assessment on a regular basis
(e.g., after each five to ten new accuracy measurements).
9.4 Laboratory blanks—Laboratory reagent water blanks are analyzed to demonstrate freedom from
contamination.
9.4.1 Extract and concentrate a laboratory reagent water blank initially (i.e. with the tests in
Section 9.2) and with each analytical batch. The blank must be subjected to the exact
same procedural steps as a sample.
9.4.2 If material is detected in the blank at a concentration greater than the Minimum Level
(Section 1.6), analysis of samples is halted until the source of contamination is eliminat-
ed and a blank shows no evidence of contamination.
9.5 Calibration verification—Verify calibration of the balance per Section 10 before and after each
analytical batch of 14 or fewer measurements. (The 14 measurements will normally be 10
samples, 1 blank, 1 OPR, 1 MS, and 1 MSD.) If calibration is not verified after the measure-
ments, recalibrate the balance and reweigh the batch.
9.6 Ongoing precision and recovery—To demonstrate that the analysis system is in control, and
acceptable precision and accuracy is being maintained with each analytical batch, the analyst
shall perform the following operations:
9.6.1 Extract and concentrate a precision and recovery standard (Section 7.11) with each
analytical batch according to the procedure beginning in Section 11.
9.6.2 Compare the concentration with the limits for ongoing precision and recovery in Table 1.
If the concentration is in the range specified, the extraction, evaporation, and weighing
processes are in control and analysis of blanks and samples may proceed. If, however,
the concentration is not in the specified range, the analytical process is not in control. In
this event, correct the problem, re-extract the analytical batch, and repeat the ongoing
precision and recovery test.
9.6.3 The laboratory should add results that pass the specification in Section 9.6.2 to IPR and
previous OPR data and update QC charts to form a graphic representation of continued
laboratory performance. The laboratory should also develop a statement of laboratory
data quality for each analyte by calculating the average percent recovery (R) and the
standard deviation of percent recovery (s 1 ). Express the accuracy as a recovery interval
12
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Method 1664
from R — 2 Sr to R + 2 Sr. For example, if R 95% and Sr = 5%, the accuracy is 85% to
105%.
9.7 Quality control sample (QCS)—it is suggested that the laboratory obtain a quality control sample
from a source different from the source for the hexadecane and stearic acid used routinely in this
method (Sections 7.8 and 7.9), and that the QCS be used for verification of the concentrations of
HEM and SGT-HEM using the procedure given in the note in Section 7.10.3.
9.8 The specifications contained in this method can be met if the apparatus used is scrupulously
cleaned and dedicated for the determination of HEM and SGT-HEM. The standards used for
initial precision and recovery (IPR, Section 9.2.2), matrix spikes (MSIMSD, Section 9.3), and
ongoing precision and recovery (OPR, Section 9.6) should be identical, so that the most precise
results will be obtained.
9.9 Depending upon specific program requirements, field replicates and field spikes into samples
may be required to assess the precision and accuracy of the sampling and sample transporting
techniques.
10.0 Calibration and Standardization
10.1 Calibrate the analytical balance at 10 mg and 1000 mg using class “S” weights.
10.2 Calibration shall be within ± 10% (i.e. 0.5 mg) at 5 mg and ± 0.5% (i.e. 5 mg) at 1000 mg. If
values are not within these limits, recalibrate the balance.
11.0 Procedure
This method is entirely empirical. Precise and accurate results can be obtained only by strict adher-
ence to all details.
Note: The procedure below is based on the preparation, extraction, and analysis of a I L
sample volume, if a smaller volume of sample is collected for analysis, the laboratory may need
to adjust the size of the labware used in order to compensate for the smaller volume being
processed. Commensurately smaller volumes of reagents (i.e. HG! or H 2 S0 4 ., n-hexane, and
sodium sulfate) may be used.
11.1 Preparation of the analytical batch.
11.1.1 Bring the analytical batch of samples, including the sample aliquots for the MS and
MSD, to room temperature.
11.1.2 Place approximately 1000 mL (950—1050 mL) of reagent water (Section 7.1) in a clean
sample bottle to serve as the laboratory blank.
11.1.3 Prepare the OPR (Section 9.6) using the PAR standard (Section 7.11).
11.1.4 Either mark the sample bottles at the water meniscus or weigh the bottles for later
determination of sample volume. Weighing will be more accurate. Mark or weigh the
MS and MSD.
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Method 1664
11.2
pH verification.
11.2.1
Verify that the pH of the sample is <2 using
the following procedure:
11.2.1.1 Dip a glass stirring rod into the well
mixed sample.
11.2.1.2 Withdraw the stirring rod and allow
pH paper.
a drop of the sample to fall
on
or touch
the
Note:
Do not dip the pH paper into the bottle or touch it to the sample on the lid.
11.2.1.3 Rinse the stirring rod with a small portion of n-hexane that will be used for
extraction (to ensure that no extractable material is lost on the stirring rod).
Collect the rinsate in the separatory funnel to be used for sample extraction.
11.2.2 If the sample is at neutral pH, add 4-6 mL HCI or H 2 S0 4 solution (Section 7.2) to the 1
liter sample. If the sample is at high pH, use a proportionately larger amount of HC1 or
H,S0 4 solution. If a smaller sample volume was collected, use a proportionately smaller
amount of HCI or H 2 S0 4 solution.
11.2.3 Replace the cap and shake the bottle to mix thoroughly. Check the pH of the sample
using the procedure in Section 11 .2.1. If necessary, add more acid to the sample and
retest.
11.2.4 Add the appropriate amount of HC1 solution to the blank, OPR, MS, and MSD.
11.3 Extraction
11.3.1 Tare a boiling flask containing 3—5 boiling chips as follows:
11.3.1.1 Place the flask containing the chips in an oven at 105—115°C for a minimum of 2
h to dry the flask and chips.
11.3.1.2 Remove from the oven and immediately transfer to cool in a desiccator.
11.3.1.3 When cool, remove from the desiccator and weigh immediately on a calibrated
balance (Section 10).
11.3.2 Pour the sample into the separatory funnel.
11.3.3 Add 30 mL n-hexane to the sample bottle and seal the bottle with the original bottle cap.
Shake the bottle to rinse all interior surfaces of the bottle, including the lid of the bottle
cap. Pour the solvent into the separatory funnel.
11.3.4 Extract the sample by shaking the separatory funnel vigorously for 2 minutes with
periodic venting into a hood to release excess pressure.
11.3.5 Allow the organic phase to separate from the aqueous phase for a minimum of 10 min-
utes. If an emulsion forms between the phases and the emulsion is greater than one-third
the volume of the solvent layer, the analyst must employ mechanical techniques to
complete the phase separation. The optimum technique depends upon the sample, but
may include stirring, filtration through glass wool, use of solvent phase separation paper,
centrifugation, use of an ultrasonic bath with ice, addition of NaCl, or other physical
14
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Method 1664
methods. Alternatively, solid-phase or other extraction techniques may to
prevent emulsion formation, provided that the requirements in Section 9.1.2 are met.
11.3.6
Drain the aqueous layer (lower layer) into the original sample container. Drain a small
amount of the organic layer into the sample container to minimize the amount of water
remaining in the separatory funnel.
Note: The amount of water remaining with the n-hexane must be minimized to prevent dissolu-
tion or clumping of the sodium sulfate in the solution drying process.
11.3.7 Place approximately 10 g anhydrous Na 2 SO 4 in a filter funnel and rinse with a small
portion of n-hexane. Discard the rinsate.
Note: The specific properties of a sample may necessitate the use of larger amounts of
Na,S0 4 .
11.3.8 Drain the n-hexane layer (upper layer) from the separatory funnel through the Na ,S0 4
into the preweighed boiling flask containing the boiling chips (Section 11.3.1.3).
11.3.9 Repeat the extraction (Sections 1 1.3.3—I 1.3.6 and 11.3.8) twice more with fresh 30-mL
portions of n-hexane, combining the extracts in the boiling flask.
11.3.10 Rinse the tip of the separatory funnel, the filter paper, and the funnel with 2—3 small
(3—5 mL) portions of n-hexane. Collect the nnsings in the flask.
11.3.11 A milky extract indicates the presence of water. If the extract is milky, allow the solu-
tion to settle for up to one hour to allow the water to sink to the bottom. Decant the
solvent layer (upper layer) through sodium sulfate to remove any excess water as in
Sections 11.3.7—11.3.8.
11.3.12 If SGT-HEM only is to be determined, proceed to Section 11.5.
11.4 Solvent evaporation.
11.4.1 Connect the boiling flask to the distilling head apparatus and evaporate the solvent by
immersing the lower half of the flask in a water bath or a steam bath. Adjust the water
temperature as required to complete the concentration in less than 30 minutes. Collect
the solvent for reuse.
11.4.2 When the temperature in the distilling head reaches 70°C or the flask appears almost dry,
remove the distilling head. Sweep out the flask for 15 seconds with air to remove
solvent vapor by inserting a glass tube connected to a vacuum source. Immediately
remove the flask from the heat source and wipe the outside surface dry to remove excess
moisture and fmgerprints.
Note: The analyst should carefully monitor the flask during the final evaporation stages to
assure that all of the solvent is removed and at the same time to prevent loss of the more volatile
sample constituents. ______________________________________________________
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Method 1664
11.4.3 Inspect the residue in the boiling flask for crystals. Crystal fonnation is an indication
that sodium sulfate may have dissolved and passed into the tared boiling flask. This may
happen when the drying capacity of the sodium sulfate is exceeded or if the sample was
not adjusted to low pH. If crystals are observed, redissolve the extract in n-hexane, filter
into another tared boiling flask, and repeat the evaporation procedure (Sections 11.4.1—
11.4.2).
11.4.4 Cool the boiling flask in a desiccator for at least 30 minutes and determine the weight of
the material in the flask.
11.4.4.1 If the extract was from the HEM procedure, determine the HEM (Wh) by sub-
tracting the tare weight (Section 11.3.1) from the total weight of the flask.
11.4.4.2 If the extract was from the SGT-HEM procedure (Section 11.5.5), determine the
weight of SGT-HEM (Wa) by subtracting the tare weight from the total weight of
the flask.
11.4.5 Determine the original sample volume (Vs) in liters by filling the sample bottle to the
mark with water and measuring the volume of water in a 1 to 2 L graduated cylinder. If
the sample weight was used (Section 11.1.4), weigh the empty bottle and cap and deter-
mine V, by difference, assuming a sample density of 1.00.
11.5 SOT-HEM determination.
11.5.1 Silica gel capacity—To ensure that the capacity of the silica gel will not be exceeded, the
amount of HEM must be known.
11.5.1.1 If it is known that the amount of HEM is less than 100 mg, the analyst may
proceed with the determination of SOT-HEM per Sections 11.5.3—11.5.5 without
determination of HEM.
11.5.1.2 If, however, the amount of HEM is not known, HEM must first be determined
using the procedure in Sections 11.3—11.4.
11.5.2 Extractable materials in silica gel—Because the capacity of silica gel is not known for all
substances, it is presumed that 3 g will adsorb 100 mg of all adsorbable materials. The
amount of silica gel that can be used for adsorption in the SGT-HEM procedure below
has been limited to 30 g because of concerns about possible extractable impurities in the
silica gel. Therefore, if the extract contains more than 1000 mg of HEM, split the
extract per the following procedure:
11.5.2.1 Add 85—90 mL of n-hexane to the boiling flask to redissolve the HEM. If neces-
saly, heat the solution on an explosion-proof hotplate or in a water bath to com-
pletely redissolve the HEM.
11.5.2.2 Transfer the extract to a 100-mL volumetric flask. Rinse the boiling flask se-
quentially with 2—3 small poitions of n-hexane and add to the volumetric flask.
Dilute to the mark with n-hexane.
11.5.2.3 Calculate the extract volume that contains 1000 mg of extractable material ac-
cording to the following equation:
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Method 1664
Equation 4
1000 V
V
a
w
where:
Va = Volume of aliquot to be withdrawn (mL)
V Total volume of solvent used in Section 11.5.2.2 (mL)
Wh Weight of extractable material HEM measurement (mg)
11.5.2.4 Using a calibrated pipet, remove the volume to be withdrawn (Va) and return to
the boiling flask. Dilute to approximately 100 mL with n-hexane.
11.5.3 Adsorption with silica gel
11.5.3.1 Add 3.0 ± 0.3 g of anhydrous silica gel (Section 7.7) to the boiling flask for
every 100 mg of HEM, or fraction thereof, to a maximum of 30 g of silica gel.
For example, if the weight of HEM is 735 mg, add 3 x 8 = 24 g of silica gel.
11.5.3.2 Add a PTFE-coated stirring bar to the flask and stir the solution on a magnetic
stirrer for a minimum of 5 minutes.
11.5.4 Filter the solution through n-hexane moistened filter paper into a pre-dried, tared boiling
flask containing several boiling chips. Rinse the silica gel and filter paper with several
small amounts of n-hexane to complete the transfer.
11.5.5 Evaporate the solution and determine the weight of SGT-HEM per Section 11.4.
12.0
Data Analysis and Calculations
12.1
n-Hexane extractable material—Calculate the concentration of HEM (“oil and grease”) in the
sample per the following equation:
Equation 5
W (mg)
HEM (mg/L) = h -
V 5 (L)
where:
Wh = Weight of extractable material Section 11.4.4.1 (mg)
V 5 = Sample volume from Section 11.4.5 (L)
12.2 Silica gel treated n-hexane extractable material—Calculate the concentration of SGT-HEM
(“petroleum hydrocarbons”) in the sample per the equation above, substituting W (from Section
11.4.4.2) for Wh. If the extract was split to decrease the total amount of material to 1,000 mg,
17
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Method 1664
determine the corrected total weight of SGT-HEM in the un-split extract (We) using the follow-
ing equation:
Equation 6
V
W (mg) = _.L Wd (mg)
where:
W , = Weight in the portion of the extract split for adsorption (Sections 11.5.2.4 and 11.4.4.2)
V 1 and V 0 are as defined in Equation 3
Use the corrected total weight of SGT-HEM in the unsplit extract (We) to determine the total
SGT-HEM in the sample by substituting W for Wh in Equation 5.
12.3 Reporting
12.3.1 Samples—Report results to three significant figures for FIEM and SGT-HEM found
above the Minimum Level (Section 1.6) in all samples. Do not report results below the
Minimum Level.
12.3.2 Report results to three significant figures for HEM and SGT-HEM found above the
Method Detection Limit (Section 1.6) in all blanks. Do not report results below the
MDL.
13.0 Method Performance
This method was validated in 13 laboratories using spiked reagent water samples (References 16.1,
16.2, and 16.9).
14.0 Pollution Prevention
14.1 The solvents used in this method pose little threat to the environment when recycled and man-
aged properly.
14.2 Standards should be prepared in volumes consistent with laboratory use to minimize the volume
of expired standards to be disposed.
15.0 Waste Management
15.1 It is the laboratory’s responsibility to comply with all federal, state, and local regulations govern-
ing waste management, particularly the hazardous waste identification rules and land disposal
restrictions, and to protect the air, water, and land by minimizing and controlling all releases
from fume hoods and bench operations. Compliance with all sewage discharge permits and
regulations is also required.
15.2 Samples preserved with HCI or H 2 S0 4 to pH < 2 are hazardous and must be neutralized before
being disposed, or must be handled as hazardous waste.
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Method 1664
15.3 For further information on waste management, consult “The Waste Management Manual for
Laboratory Personnel”, and “Less is Better: Laboratory Chemical Management for Waste
Reduction”, both available from the American Chemical Society’s Department of Government
Relations and Science Policy, 1155 16th Street N.W., Washington, D.C. 20036.
16.0 References
16.1 “Determination of the Method Detection Limit and Minimum Level for EPA Method 1664 by
Global Environmental Services”, October 1994. Available from the Sample Control Center
(operated by DynCorp Viar), 300 North Lee Street, Alexandria, VA 22314, (703) 519-1140.
16.2 “Summary Results from Phase II of the Freon Replacement Study for work performed by Com-
monwealth Technology, Inc. under Special Analytical Services Contract 1273”, January 1, 1994.
Available from the Sample Control Center (operated by DynCorp Viar), 300 N. Lee St., Alexan-
dria, VA 22314, (703) 519-1140.
16.3 40 CFR 136, Appendix A, Methods 1624 and 1625.
16.4 “Carcinogens - Working With Carcinogens,” Department of Health, Education, and Welfare,
Public Health Service, Center for Disease Control, National Institute for Occupational Safety and
Health, Publication No. 77-206, August 1977.
16.5 “OSHA Safety and Health Standards, General Industry,’ (29 CFR 1910), Occupational Safety
and Health Administration, OSHA 2206 (Revised, January 1976).
16.6 “Safety in Academic Chemistry Laboratories,” American Chemical Society, Committee on
Chemical Safety, 3rd Edition, 1979.
16.7 “Standard Practices for Sampling Water,” ASTM Annual Book of Standards, Part 31, D3370-76,
American Society for Testing and Materials, 1916 Race Street, Philadelphia, PA 19103-1187,
1980.
16.8 “Handbook of Analytical Quality Control in Water and Wastewater Laboratories,” USEPA,
EMSL-Ci, Cincinnati, OH 45268, EPA-600/4 -79-019, March 1979.
16.9 “Results of the Twin City Round Robin Group Interlaboratory Study of Method 1664 HEM
analysis”, October 1994. Available from the Sample Control Center (operated by DynCorp
Viar), 300 N. Lee Street, Alexandria, VA 22314, (703) 519-1140.
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Method 1664
17.0 Tables
Table 1. Acceptance Criteria for Pertormance Tests
Acceptance Criterion Section
Limit
ln ial precision and recovery
HEM Precision (s)
HEM Recovery (X)
SGT-HEM Precision (s)
S 3T-HEM Recovery (X)
10 percent
83—101 percent
13 percent
83-116 percent
Matrix spike/matrix spike duplicate
HEM Recovery
HEM RPD
SGT-HEM Recovery
SGT-HEM RPD
9.3
9.3.4
9.3.5
9.3.4
9.3.5
79—114 percent
18 percent
66-114 percent
24 percent
Ongoing precision and recovery
HEM Recovery
SGT-HEM Recovery
9.6
9.6
9.6
79-114 percent
66—114 percent
9.2.2
9.2.2.2
9.2.2.2
9.2.2.2
9.2.2.2
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Method 1664
18.0 Glossary of Definitions and Purposes
The definitions and purposes are specific to this method but have been conformed to common usage as
much as possible.
18.1 Units of weight and measure and their abbreviations
18.1.1 Symbols
°C degrees Celsius
less than
% percent
± plus or minus
18.1.2 Alphabetical characters
g gram
h hour
L liter
mg milligram
mg/g milligram per gram
mgIL milligram per liter
mg/mL milligram per milliliter
mL milliliter
No. number
rpm revolutions per minute
18.2 Defmitions, acronyms, and abbreviations
18.2.1 Analyte : The HEM or SGT-HEM tested for by this method.
18.2.2 Analytical batch : The set of samples extracted at the same time, to a maximum of 10
samples. Each analytical batch of 10 or fewer samples must be accompanied by a
laboratory blank (Section 9.4), an ongoing precision and recovery sample (OPR, Section
9.6), and a matrix spike and matrix spike duplicate (MSIMSD, Section 9.3), resulting in
a minimum of five analyses (1 sample, I blank, 1 OPR, I MS, and I MSD) and a
maximum of 14 analyses (10 samples, 1 blank, 1 OPR, 1 MS, and I MSD) in the batch.
If greater than 10 samples are to be extracted at one time, the samples must be separated
into analytical batches of 10 or fewer samples.
18.2.3 Field blank : An aliquot of reagent water that is placed in a sample container in the
laboratory or in the field and treated as a sample in all respects, including exposure to
sampling site conditions, storage, preservation, and all analytical procedures. The pur-
pose of the field blank is to determine if the field or sample transporting procedures and
environments have contaminated the sample.
18.2.4 HEM : See n-Hexane extractable material.
18.2.5 n-Hexane extractable material : The material that is extracted from a sample and deter-
mined by this method.
18.2.6 IPR : See initial precision and recovery.
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Method 1664
18.2.7 Initial precision and recovery (IPR) : Four aliquots of the diluted PAR analyzed to
establish the ability to generate acceptable precision and accuracy. An IPR is performed
the first time this method is used and any time the method or instrumentation is modi-
fied.
18.2.8 Laboratory blank (method blank) : An aliquot of reagent water that is treated exactly as a
sample including exposure to all glassware, equipment, solvents, reagents, internal
standards, and surrogates that are used with samples. The laboratory blank is used to
determine if analytes or interferences are present in the laboratory environment, the
reagents, or the apparatus.
18.2.9 Laboratory control sample (LCS) : See Ongoing precision and recovery standard (OPR).
18.2.10 Matrix spike (MS) and matrix spike duplicate (MSD) : Aliquots of an environmental
sample to which known quantities of the analytes are added in the laboratory. The MS
and MSD are prepared and/or analyzed exactly like a field sample. Their purpose is to
quantify any additional bias and imprecision caused by the sample matrix. The back-
ground concentrations of the analytes in the sample matrix must be determined in a
separate aliquot and the measured values in the MS and MSD corrected for background
concentrations.
18.2.11 May : This action, activity, or procedural step is neither required nor prohibited.
18.2.12 May not : This action, activity, or procedural step is prohibited.
18.2.13 Method Detection Limit : The lowest level at which an analyte can be detected with 99
percent confidence that the analyte concentration is greater than zero.
18.2.14 Minimum Level (ML) : The lowest level at which the entire analytical system gives a
recognizable signal and acceptable calibration point for the analyte. It is equivalent to
the concentration of the lowest calibration standard, assuming that all method-specified
sample weights, volumes, and cleanup procedures have been employed.
18.2.15 Must : This action, activity, or procedural step is required.
18.2.16 Ongoing precision and recovery standard (OPR, also called a laboratory control sample) :
A laboratory blank spiked with known quantifies of analytes. The OPR is analyzed
exactly like a sample. Its purpose is to assure that the results produced by the laboratory
remain within the limits specified in this method for precision and accuracy.
18.2.17 OPR : See Ongoing precision and recovery standard.
18.2.18 PAR : See Precision and recovery standard.
18.2.19 Precision and recovery standard : Secondary standard that is diluted and spiked to form
the IPR and OPR.
18.2.20 Quality control sample (OCS) : A sample containing analytes of interest at known
concentrations. The QCS is obtained from a source external to the laboratory or is
prepared from standards obtained from a different source than the calibration standards.
The purpose is to check laboratory performance using test materials that have been
prepared independently from the normal preparation process.
22
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Method 1664
18.2.21 Reagent water : Water demonstrated to be free from HEM and SGT-HEM and potentially
interfering substances at or above the Minimum Level of this method.
18.2.22 SGT-HEM : See Silica gel treated n-hexane extractable material.
18.2.23 Should : This action, activity, or procedural step is suggested but not required.
18.2.24 Silica gel treated n-hexane extractable material : n-Hexane extractable material (HEM)
that is not adsorbed by silica gel.
18.2.25 Stock solution : A solution containing an analyte that is prepared using a reference
material traceable to EPA, the National Institute of Science and Technology (NIST), or a
source that will attest to the purity and authenticity of the reference material.
23
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