United States Office of Water
Environmental Protection Agency (4303)
February 2010
4>EPA Method 1664, Revision B: n-Hexane
Extractable Material (HEM; Oil and
Grease) and Silica Gel Treated
n-Hexane Extractable Material
(SGT-HEM; Non-polar Material) by
Extraction and Gravimetry
February 2010
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U.S. Environmental Protection Agency
Office of Water (4303T)
1200 Pennsylvania Avenue, NW
Washington, DC 20460
EPA-821-R-10-001
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Method 1664. Revision B
Acknowledgments
Revision B of this method was prepared by the Engineering and Analysis Division within EPA's Office
of Water. EPA gratefully acknowledges assistance from DynCorp Information and Enterprise
Technology in the preparation of the earlier versions. Additionally, EPA gratefully acknowledges
Xenosep Technologies for their comments and review.
Disclaimer
This method has been reviewed by the Engineering and Analytical Support Branch of the Engineering
and Analysis Division (EAD) in OST and approved for publication. Mention of trade names or
commercial products does not constitute and endorsement or recommendation for use.
Contact
Questions concerning this method or its application should be directed to:
CWA Methods Team, or Lemuel Walker
U.S. EPA
Engineering and Analysis Division, MC 4303T
Office of Science and Technology
1200 Pennsylvania Avenue NW
Washington, D.C. 20460
OSTCWAMethods@epa.gov
Walker.Lemuel@epa.gov
Additional copies of this method are available at: http://www.epa.gov/waterscience/methods/
February 2010
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Method 1664. Revision B
Table of Contents
Introduction Ill
1.0 Scope and Application ±
3.0 Definitions 5
4.0 Interferences 5
5.0 Safety 7
6.0 Equipment and Supplies 7
7.0 Reagents and Standards 10
8.0 Sample Collection, Preservation, and Storage n
9.0 Quality Control 12
10.0 Calibration and Standardization 19
11.0 Procedure 19
12.0 Data Analysis and Calculations 24
13.0 Method Performance 25
14.0 Pollution Prevention 25
15.0 Waste Management 25
16.0 References 26
17.0 Tables 27
18.0 Glossary of Definitions and Purposes 27
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Method 1664. Revision B
Introduction
EPA withdrew all oil and grease methods using chlorofluorocarbon-113 (CFC-113; Freon-113) as an
extraction solvent in the final rule published March 7, 2007; 72 FR 11199, including approved Method
413.1, and Methods 418.1 and 418.2, which were never approved for use at 40 CFR 136 even though they
were listed in the now outdated Methods for Chemical Analysis of Water and Wastes (EPA 600/4-79-
020; NTIS PB84-128677). As such, EPA Method 1664, Revision B: n-Hexane Extractable Material
(HEM; Oil and Grease) and Silica Gel Treated n-Hexane Extractable Material (SGT-HEM; Non-polar
Material) is the only approved EPA method for the measurement of oil and grease.
The term "n-Hexane Extractable Material (HEM; Oil and Grease)" reflects the material extracted by n-
hexane as that which is being measured using Method 1664 and that the common name "oil and grease" is
being retained because of its familiarity to the analytical community. The term "Silica-gel Treated n-
Hexane Extractable Material (SGT-HEM; Non-polar Material)" designates the substances that remain
after n-hexane extractable material is exposed to silica gel. In the final rule published May 14, 1999 (64
FR 26315) the term "Non-polar Material" (NPM) was chosen to avoid confusion in the analytical
community with the term "total petroleum hydrocarbons" (TPH), as this term can measure a different
property or material, or employ different analytical techniques, including infrared spectroscopy and gas
chromatography.
Method 1664B is a performance-based method applicable to the measurement of the method-defined
parameters HEM and SGT-HEM from aqueous matrices and requires the use of n-hexane as the
extraction solvent, gravimetry as the determinative technique, and includes additional QC procedures
designed to monitor precision and accuracy. Although analyst modification of an approved, method-
defined analyte method is generally not allowed, some performance-based changes may be acceptable.
However, it should be noted that due to the nature of some discharge/waste streams, not all samples may
be amenable to analysis with a modified method, (e.g., SPE as the modification) and for these samples,
1664B should be applied as written.
The purpose of this update is to provide additional information to improve method performance and more
clearly define by example:
1. Modifications that are allowed for nationwide use without prior EPA review (40 CFR 136.6).
2. Modifications that are not allowed.
The modifications listed below and included in Section 1.7 are not meant to be an exhaustive list of all
possible modifications to the method, but rather they represent modifications which have been presented
to the EPA by various stakeholders and our determination of their acceptability for use in Method 1664B.
In recognition of advances that are occurring in analytical technology, the laboratory 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 continuous liquid-liquid extraction (CLLE), evaporation, Kuderna-Danish
concentration and solid-phase extraction (SPE). Alternate determinative techniques, such as
immunoassay and infrared spectroscopy, and changes that degrade method performance or change the
chemistry of the method including the use of extraction solvents other than n-hexane (85% minimum
purity, 99.0% min. saturated C6 isomers, residue less than 1 mg/L - see Section 7.3) 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. Specificity is defined as producing results equivalent to the results
produced by this method for analytical standards (Section 9.2.2) and, where applicable, environmental
samples (Section 9.2.3), and that meet all of the QC criteria stated in this method. 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. Revision B
Method 1664, Revision B
n-Hexane Extractable Material (HEM; Oil and Grease) and
Silica Gel Treated n-Hexane Extractable Material (SGT-HEM;
Non-polar Material) by Extraction and Gravimetry
1.0 Scope and Application
1.1 This method is for determination of n-hexane extractable material (HEM; oil and grease) and n-
hexane extractable material that is not adsorbed by silica gel (SGT-HEM; non-polar material) 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. The method is based on prior Environmental Protection
Agency (EPA) methods for determination of "oil and grease" and "total petroleum hydrocarbons"
(References 16.1 and 16.2).
1.2 This method is for use in the Environmental Protection Agency's (EPA's) survey and monitoring
programs under the Clean Water Act; the Resource Conservation and Recovery Act; the
Comprehensive Environmental Response, Compensation, and Liability Act; and other EPA
regulatory programs. "Oil and grease" is a conventional pollutant under the Clean Water Act and
codified at 40 CFR 401.16. The term "n-hexane extractable material" reflects that this method
can be used to determine materials other than oils and greases. Similarly, the term "silica gel
treated n-hexane extractable material" reflects that this method can be used to determine material
that is not adsorbed by silica gel (non-polar material).
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 and SGT-HEM in the range of 5 to 1000 mg/L, and
may be extended to higher levels by analysis of a smaller sample volume collected separately.
1.6 For HEM and SGT-HEM in this method, the method detection limit (MDL) is 1.4 mg/L and the
minimum level of quantitation (ML) is 5.0 mg/L (Reference 16.3).
1.7 The laboratory is permitted to modify the method to overcome 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 Sections 9.1.2 and 9.2.3.
Some examples of allowed and unacceptable modifications include:
1.7.1 Allowable Modifications
1.7.1.1 Alternate extraction techniques including continuous liquid-liquid extraction,
solid-phase extraction, solid-phase-heated solvent extraction, solid-phase-
Soxhlet extraction, and others. Acceptable solid-phase extraction (SPE)
products include: Xenosep filters for EPA Method 1664, part no. 24547 and
25390H or equivalent; UCT LLC Oil and Grease cartridge part no.
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Method 1664. Revision B
ECUNIOGXF, or equivalent; or other SPE products that meet all method
performance criteria such as Horizon part no. 50-021-HT, Snip and Pour QC
Standard or equivalent.
1.7.1.2 Alternate concentration techniques including Kuderna-Danish concentration
and evaporation using aluminum pans, beakers and flasks as well as user
defined temperatures and approximate concentration times.
1.7.1.3 The requirement to dry the boiling flask for 30-45 minutes in an oven
maintained at 70 ± 2 °C at Section 11.4.2.2 may be completely omitted or
replaced with a user-defined lower temperature and/or shorter drying time.
1.7.1.4 A lower PAR (Precision and Recovery) standard concentration such as
20 mg/L may be used to spike matrix samples provided the concentration of
the spike is: (a) greater than the background concentration, (b) less than or
equal to the regulatory compliance level and (c) all quality control
requirements are achieved.
1.7.1.5 Collection and analysis of a smaller sample volume is permitted provided all
the quality control requirements of Section 9 are met. If smaller sample
volumes are used, all QC and initial and ongoing demonstration of
performance samples must use the same volume as the smaller volume
samples. To achieve a proportionately smaller matrix spike at the
recommended OPR concentration of 40 mg/L, i.e., spike 0.1 mL of the
4 mg/mL PAR standard for every 10 mL of proportionately smaller sample
volume or fraction thereof. To report the most accurate HEM and SGT-
HEM values in mg/L, subtract the smaller volume method blank value from
the smaller volume sample value provided the recovery value of the smaller
volume matrix spike is equal to or greater than the MDL for the modified
method. Multiply this proportionately smaller sample value by the
appropriate dilution factor and express the final sample result in mg/L. For
example, if 4.4 mg/100 mL was the result for the proportionately smaller
sample and 0.6 mg/lOOmL was the result for the method blank, the reported
concentration of the sample should be 38.0 mg/L ([4.4 mg/100 mL - 0.6
mg/100 mL] x 10 = 38.0 mg/L). Additionally, all samples must be
associated with an uncontaminated, 1-L method blank before the results
may be reported for regulatory compliance purposes.
1.7.1.6 Balances should be calibrated with an additional upper class "S" weight in
order to bracket the expected final weighing value. In addition, the
frequency of balance calibration per Section 9.5 may be modified to before
and after each day provided all QC requirements are achieved and the
laboratory accepts responsibility for their results.
1.7.1.7 All samples must be acidified and/or verified in the lab to pH<2 immediately
prior to analysis. If analysis is to be delayed for more than four hours, adjust
the sample in the field to pH<2 with HC1 or H2SO4 solution (Section 7.2) at
the time of collection and refrigerate to 0-6 °C (40 CFR 136, Table II). If the
sample is to be shipped by commercial carrier, U.S. Department of
Transportation regulations (see 49 CFR Part 172) limit the pH to a minimum
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Method 1664. Revision B
of 1.96 if HC1 is used and 1.15 if H2SO4 is used. (See 40 CFRPart 136,
Table II Footnote 3).
1.7.1.8 The use of optional prefilters, filtration aids, glass wool and/or other means
including centrifugation and sedimentation to aid processing of specific
samples is allowed per Section 11.3.5. As appropriate, samples acidified to
pH<2 which have settled upon refrigerated storage may be analyzed "as is"
instead of first mixing and then centrifuging the sample in order to achieve a
similar, settled physical state prior to analysis.
1.7.1.9 If SPE filters are used in the analytical batch, they must all be of the same
manufacturer brand and diameter. If different manufacturer's brand or
different diameter SPE filters are used in different analytical batches or
methods, each different SPE method must have its own quality control chart.
1.7.1.10 The laboratory may randomly choose at least one representative
discharge/waste stream for the matrix spike for every batch of samples
analyzed and must keep a running record of their selection. However, the
laboratory may not use the same discharge/waste stream for the matrix spike
as was used in the immediately previous batch unless the laboratory only
analyzes one discharge/waste stream. If the same discharge/waste stream is
selected, the laboratory should randomly select the matrix spike from
discharges/waste streams not used for the immediately previous batch.
1.7.1.11 Use of repetitive treatments with silica gel is allowed, as well as using lower
amounts, provided the minimum treatment ratio of 3 g silica gel for every
100 mg HEM is maintained, per Section 11.5.
1.7.1.12 The use of solvent phase separation paper or other equivalent means may be
used instead of sodium sulfate to remove water from the extract, provided all
QC requirements are met, especially Sections 9.3 and 9.4, matrix spike and
laboratory blanks respectively.
1.7.1.13 The use of silica gel equivalent to that specified at Section 7.7 may be used,
provided all QC performance criteria in this method are met.
1.7.1.14 The use of an optimized extract shaking time (Section 11.3.4) and/or an
optimized number of n-hexane extractions (Section 11.3.9) is allowed,
provided all QC performance criteria in this method are achieved.
1.7.1.15 The hexadecane and stearic acid reference standards may be stored in the
dark in an explosion-proof refrigerator to help prevent acetone evaporation
provided: 1) The room temperature volume level is clearly marked on the
container and 2) The standard is allowed to re-equilibrate to room
temperature before use.
1.7.1.16 Rinsing bottles or apparatus with a polar solvent for glassware cleaning
(Section 6.1.2), or other purposes, is allowed, provided the solvent: 1) is
immediately sent to waste, 2) is sufficiently removed from contact surfaces
so it will not introduce the target analyte into the sample, 3) will not collocate
with the extraction solvent n-hexane and 4) will not be collected into the
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Method 1664. Revision B
collection vessel. See Section 1.7.2.1 and the note below that section for
additional SPE apparatus requirements.
1.7.1.17 Samples may be analyzed within a user-defined, controlled temperature
range to improve extraction efficiency, provided all samples (including QC)
are analyzed under similar conditions and all QC performance criteria in this
method are achieved.
1.7.2 Unacceptable Modifications
1.7.2.1 The extraction solvent must be n-hexane (85% minimum purity, 99.0% min.
saturated C6 isomers, residue less than 1 mg/L - see Section 7.3). Alternate
extraction solvents or co-solvents including methanol, acetone and others
that react with or introduce the target pollutant into the sample are not
allowed.
However, a methanol or other polar solvent rinse after sample filtration may
be allowed to remove water residual when using SPE technology in a
modified method provided:
1. The methanol rinse is immediately discarded to waste.
2. The SPE filter is sufficiently air dried with vacuum to remove any
residual methanol remaining in the SPE filter to trace amounts so as to
ensure residual methanol will not introduce the target analyte into the
sample and at no time will residual methanol collocate with or be
collected with the n-hexane extractions.
3. The laboratory must demonstrate and document the appropriate operating
conditions (1 & 2) above to allow this use of methanol.
NOTE: The use of a polar solvent to condition an SPE filter or SPE device in a modified method prior to
sample filtration is allowed. The use of methanol or another polar solvent after sample filtration to
remove water residual may be allowed provided the polar solvent is immediately discarded to waste and
the SPE filter or SPE device is sufficiently air-dried with vacuum to remove any residual polar solvent to
trace amounts so at no time will residual polar solvent introduce the target analyte into the sample,
collocate with or be collected with the extraction solvent, n-hexane. A simple test to determine sufficient
residual polar solvent removal from an SPE filter by vacuum air drying would be to weigh and record the
weight of a dry SPE filter to the nearest 0.1 mg. Then analyze a blank using the dry SPE filter,
conditioning the SPE filter and filtering the blank sample per the modified SPE method. Immediately
after discarding the polar solvent to waste (and prior to addition of the n-hexane extraction solvent), stop
the vacuum, remove the SPE filter from the apparatus and weigh the wet SPE filter saturated with residual
polar solvent to the nearest 0.1 mg. Record this wet SPE filter weight. Reassemble the wet SPE filter
into the apparatus and continue vacuum air drying the SPE filter until the weight of the wet SPE filter is
less than 101% of the dry SPE filter weight. For example, if the weight of the dry SPE filter is 1,000.0
mg, continue vacuum air drying the wet SPE filter until the final weight is less than or equal to 1,010.0
mg before contacting the SPE filter with the extraction solvent n-hexane. This simple test could be used
by the laboratory to demonstrate and document removal of residual methanol from the SPE filter to trace
amounts so as to ensure residual methanol will not introduce the target analyte into the sample and at no
time will residual methanol collocate with the n-hexane extraction solvent or be collected in the collection
flask.
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Method 1664. Revision B
1.7.2.2 Alternate determinative techniques such as infrared spectroscopy or
immunoassay, and changes that degrade method performance are not
allowed.
NOTE: EPA Methods 418.1 and 418.2, which employed CFC-113 as the extraction solvent and infrared
spectroscopy and gravimetry respectively as the determinative technique, were never approved for use at
40 CFR Part 136, even though they were listed in Methods for Chemical Analysis of Water and Wastes
(EPA 600/4-79-020; NTIS PB84-128677). In the final rule published March 12, 2007; 72 FR 11199,
EPA withdrew approval of all oil and grease methods that employed chloroflurocarbon-113 (CFC-113,
Freon-113) as the extraction solvent and gravimetry or infrared spectroscopy as the determinative
technique.
1.7.2.3 Due to the non-homogeneous nature of wastewater samples and the high
probability that extractable material may contact and adhere to a wide variety
of surfaces (including substances in the sample as well as the sample bottle
and cap) and be non-uniformly distributed throughout the sample, sub-
sampling or analysis of less than the total collected volume of sample is not
allowed.
1.7.2.4 A change in the n-hexadecane and stearic acid standards is not allowed
because the performance data for this method were developed using these
reference standards.
1.7.2.5 Spiking of the n-hexadecane and stearic acid standards into the extractor
(separatory funnel, CLLE body, SPE reservoir, etc.) to potentially improve
recovery of the matrix spike is not allowed, as acceptable recovery of the
matrix spike from the sample container must be demonstrated per Section
9.3.2.2 (Reference 16.10)
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.
NOTE: Laboratories or dischargers in or regulated by EPA Region 8 may apply to Region 8 for a limited
use ATP application to use modified Method 1664 "Cu" to address colloidal sulfur or thiosulfate-inflated
results in produced water samples. In order to comply with the new regulation and be able to use
modified 1664 "Cu," the laboratory or permittee should, at a minimum:
1. Perform Method 1664B and demonstrate falsely high, out of compliance results
2. Perform modified Method 1664 "Cu" and demonstrate results in compliance with permit levels
3. Document the interference and determine the reason for the out of compliance result is due to
the presence of colloidal sulfur or thiosulfate in the specific effluent
4. Apply to Region 8 for approval of a limited use ATP application to use modified Method 1664
"Cu" instead of Method 1664B for the specific effluent.
Use of this modified method in other EPA Regions requires submission to the respective EPA Regional
Office or appropriate regulatory authority of a limited-use ATP application for approval (40 CFR 136.4
and 136.5).
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Method 1664. Revision B
1.9 Each laboratory that uses this method, with or without the allowed modifications above, must
demonstrate the ability to generate acceptable results using the procedure in Section 9.2.
2.0 Summary of Method
2.1 A 1-L sample is acidified to pH <2 and serially extracted three times with n-hexane (85%
minimum purity, 99.0% min. saturated C6 isomers, residue less than 1 mg/L - see Section 7.3) in
a separatory runnel. The extract is dried over sodium sulfate.
2.2 The solvent is distilled from the extract and the HEM is desiccated and 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 polar materials. The solution is
filtered to remove the silica gel, the solvent is distilled, and the SGT-HEM is desiccated and
weighed.
2.4 Quality is assured through calibration and testing of the extraction, distillation, and gravimetric
systems.
3.0 Definitions
3.1 HEM and SGT-HEM are method-defined analytes; i.e., the definitions of both HEM and SGT-
HEM are dependent on the procedure used and as such, the only extraction solvent allowable is n-
hexane (85% minimum purity, 99.0% min. saturated C6 isomers, residue less than 1 mg/L - see
Section 7.3) with gravimetry as the determinative technique. The use of co-solvents, alternate
solvents, or determinative techniques other than gravimetry, including infrared spectroscopy,
immunoassay, and gas chromatography, is not allowed because the chemistry of the method is
changed. 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 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.
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Method 1664. Revision B
4.4 Sodium sulfate and silica gel fines 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.
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. It is suggested that the laboratory
perform personal hygiene monitoring of each analyst that uses this method. This monitoring
should be performed using Occupational Safety and Health Administration (OSHA) or National
Institute of Occupational Safety and Health (NIOSH) approved personal hygiene monitoring
methods. Results of this monitoring should be made available to the analyst.
5.2 n-Hexane has been shown to have increased neurotoxic effects over other hexanes and some other
solvents. OSHA has proposed a time-weighted average (TWA) of 50 parts-per-million (ppm);
NIOSH concurs that an 8-hour TWA/permissible exposure limit (PEL) of 50 ppm is appropriate
for n-hexane; and the American Conference of Governmental Industrial Hygienists (ACGIH) has
published a threshold limit value (TLV) of 50 ppm for n-hexane. Inhalation of n-hexane should
be minimized by performing all operations with n-hexane in an explosion-proof hood or well-
ventilated area.
5.3 n-Hexane has a flash point of-23 °C (-9 °F), has explosive limits in air in the range of 1-7%, and
poses a serious fire risk when heated or exposed to flame. n-Hexane can react vigorously with
oxidizing materials. The laboratory should include procedures in its operations that address the
safe handling of n-hexane.
5.4 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.
5.5 This method does not address all safety issues associated with its use. The laboratory is
responsible 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 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.
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Method 1664. Revision B
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 sample known or suspected to contain >500 mg/L
of HEM (Section 8.1.2), or consisting of a complex matrix containing substances (such as particulates or
detergents) that may interfere with the extraction procedure (Section 4.5), a smaller sample container may
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 1 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.
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 ± 2 °C in the range of 20-250 °C.
6.3 Equipment for calibration
6.3.1 Analytical Balance-Capable of weighing 0.1 mg.
6.3.2 Volumetric flask-Glass, 100-mL.
6.3.3 Vials-Assorted sizes, with PTFE-lined screw caps.
6.3.4 Volumetric pipette-Glass, 10-mL.
6.4 Equipment for sample extraction
6.4.1 Balance (optional)-Top loading, capable of weighing 500-2000 g within ± 1%
6.4.2 Glass stirring rod
6.4.3 Separatory funnel-Glass, 2000-mL, with PTFE stopcock
6.4.4 Funnel-Large, glass, for pouring sample into separatory funnel
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Method 1664. Revision B
6.4.5 Centrifuge (optional)-Explosion proof, capable of spinning at least four 100-mL glass
centrifuge tubes at 2400 rpm minimum
6.4.6 Centrifuge tubes (optional)-100-mL glass
6.4.7 Wash bottle (optional)-Fluoropolymer construction for hexane rinses
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 distillation
6.6.1 Water bath or Steam bath-Explosion-proof, capable of maintaining a temperature of at
least 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
Claisen-type connecting tube and condenser
6.6.4 Distilling adaptor (attached to the distilling head and to the distillate collection flask for
recovery of solvent)
6.6.5 Distillate collection flask (attached to the distilling adaptor for collection of the distilled
solvent)
6.6.6 Ice bath or recirculating chiller (to aid in the condensation and collection of the distilled
solvent)
6.6.7 Vacuum-Vacuum pump or other source of vacuum
6.6.8 Tongs, for handling the boiling flask (Humboldt Manufacturing No. H-23442, or
equivalent)
6.6.9 Desiccator-Cabinet- or jar-type, capable of keeping the boiling flask (Section 6.6.2)
dry during cooling
6.6.10 Hood-Explosion-proof, capable of accommodating the equipment used for solvent
distillation (Section 6.6.1-6.6.5)
6.7 Equipment for removal of adsorbable materials
6.7.1 Magnetic stirrer
6.7.2 PTFE-coated magnetic stirring bars
6.7.3 Graduated cylinder-500-mL, capable of measuring ± 5 mL
6.7.4 Pipettes-Assorted sizes, calibrated to within ± 0.5 percent
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Method 1664. Revision B
7.0 Reagents and Standards
7.1 Reagent water-Water in which HEM is not detected at or above the minimum level (ML) 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 acid or sulfuric acid-ACS. Mix equal volumes of concentrated HC1 and reagent
water or 1 part H2SO4 and 3 parts reagent water to produce an approximately 6N solution
7.3 n-Hexane-85% minimum purity, 99.0% min. saturated C6 isomers, residue less than 1 mg/L
(0.0001% max.)
7.4 Acetone-ACS, residue less than 1 mg/L (0.0001% max)
7.5 Sodium sulfate-ACS, granular anhydrous. Dry at 200-250 °C for 24 h minimum and store in a
tightly sealed container until use
NOTE: Powdered sodium sulfate should not be used because traces of water may cause it to solidify.
7.6 Boiling chips-Silicon carbide or fluoropolymer
7.7 Silica gel-Anhydrous, 75-150 (im, 30 A pore size (Davisil Grade 923, 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 distilling 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 2 mg/mL
each
7.10.1 Place 200 ± 2 mg stearic acid and 200 ± 2 mg hexadecane in a 100-mL volumetric flask
and fill to the mark with acetone
NOTE: The solution may require warming for complete dissolution of stearic acid. If warmed, allow the
solution to cool back to the volume mark at room temperature before use as heat generated from vigorous
shaking can increase the volume of the solution which can cause low recovery. Best results are obtained
if the solution is allowed to cool for at least one hour after warming.
7.10.2 After the hexadecane and stearic acid have dissolved and the solution has cooled back
to the volume mark at room temperature, transfer the solution to a 100-150 mL vial
with fluoropolymer-lined cap (Kontes No. 482600-0100, or equivalent) and tighten
well the cap. Mark the solution level on the vial and store in the dark at room
temperature.
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Method 1664. Revision B
7.10.3 Immediately prior to use, verify the level on the vial and bring to volume with acetone,
if required. Warm to redissolve all visible precipitate if needed but allow the solution
to cool back to the volume mark at room temperature before use.
NOTE: If there is doubt of the concentration, remove 10.0 ±0.1 mL with a volumetric pipet, place in a
tared weighing pan, and evaporate to dryness in a fume hood. The weight must be 40 ± 1 mg. If not,
prepare a fresh solution (Section 7.10.1). Best results are obtained using large-diameter smooth-walled
aluminum weighing pans (Xenosep # 26506 or equivalent).
7.11 Precision and recovery (PAR) standard - Using a pipet, spike 10.0 ± 0.1 mL of the hexadecane/
stearic acid spiking solution (Section 7.10) into 950 - 1050 mL of reagent water to produce
concentrations of approximately 20 mg/L each of hexadecane and stearic acid. The PAR
standard is used for the determination of initial (Section 9.2.2) and ongoing (Section 9.6)
precision and recovery.
7.12 The spiking solutions should be checked frequently for signs of degradation or evaporation using
the test noted in Section 7.10.3, 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-rinsed with sample
before collection. To allow for potential QC failures, it is recommended that additional sample
aliquots be collected.
8.1.1 All samples must be acidified and/or verified in the lab to pH<2 immediately prior to
analysis. If analysis is to be delayed for more than four hours, adjust the sample pH to
less than 2 with HC1 or H2SO4 solution (Section 7.2) at the time of collection, and
refrigerate at 0-6°C (40 CFR 136, Table II). To establish the volume of HC1 or H2SO4
required, collect a separate aliquot, adjust the pH of this aliquot to less than 2 with acid,
and add the volume of acid determined to each sample bottle prior to collection.
During the sample collection, do not dip pH paper, a pH electrode, a stirring rod, or
other materials into a sample that will be used for HEM or SGT-HEM determination
because substances in the sample may adhere to these items.
8.1.2 If a sample is known or suspected to contain greater than 500 mg/L of extractable
material or consists of complex matrix containing substances (such as particulates or
detergents) that may interfere with the extraction procedure, 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 H2SO4 solution to the smaller sample for preservation as necessary.
8.2 Collect an additional one or two aliquots (1 L, additional smaller volume, or both) of a sample for
each set of twenty samples or less for the matrix spike and, if used, the 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 simultaneously in parallel, if possible, or 2)
collect as grab samples in rapid succession.
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Method 1664. Revision B
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
determination 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. Alternatively, samples can be
collected in the field and composited in the laboratory. For example, collect four individual 250-
mL samples over the course of a day. In the laboratory, pour each 250-mL sample into the
separatory funnel, rinse each of the four bottles (and caps) sequentially with 30 mL of n-hexane,
and use the 30 mL of n-hexane for the extraction (Section 11.3).
8.4 All samples must be refrigerated at 0-6 °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
performance, and analysis of a matrix spike (MS) to assess recovery. 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 laboratory 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 laboratory 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 continuous liquid-liquid
extraction, evaporation, Kuderna-Danish concentration, and solid-phase extraction.
Alternate determinative techniques, such as immunoassay or infrared spectroscopy, and
changes that degrade method performance or change the chemistry of the method
including the use of extraction solvents other than n-hexane (85% minimum purity,
99.0% min. saturated C6 isomers, residue less than 1 mg/L - see Section 7.3) 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.
Specificity is defined as producing results equivalent to the results produced by this
method for analytical standards (Section 9.2.2) and, where applicable, environmental
samples (Section 9.2.3), and that meet all of the QC criteria stated in this method.
9.1.2.1 Each time a modification is made to this method, the laboratory is required to
repeat the IPR test in Section 9.2.2 to demonstrate that the modification
produces results equivalent to or superior to results produced by this method.
If the detection limit of the method will be affected by the modification, the
laboratory must demonstrate that the MDL (40 CFR Part 136, Appendix B) is
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Method 1664. Revision B
less than or equal to the MDL in this method or one-third the regulatory
compliance limit, whichever is higher. If the modified method is to be used
for compliance monitoring, the discharger/generator must also demonstrate
that the modified method recovers an amount of HEM and/or SGT-HEM
equivalent to the amount recovered by this method on each specific
discharge/waste stream (not required for modifications allowed under
Section 1.7.1). The tests required for this equivalency demonstration are
given in Section 9.2.3.
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 (not required for modifications
allowed under Section 1.7.1).
9.1.2.2.2 A listing of pollutant(s) measured (HEM and/or SGT-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)
(f) Ongoing precision and recovery (Section 9.6)
(g) Method detection limit (Section 9.2.1).
9.1.2.2.5 Data that will allow an independent reviewer to validate each
determination 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-HEM (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 Analysis of a matrix spike (MS) is required to demonstrate recovery and to monitor
matrix interferences (interferences caused by the sample matrix). The procedure and
QC criteria for spiking are described in Section 9.3.
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Method 1664. Revision B
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 (OPR) 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 define 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. For the definition of an analytical batch, see the glossary at the end of
this method.
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 laboratory 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 or less than 1/3 the
regulatory compliance limit must be achieved prior to the practice of this method.
9.2.2 Initial precision and recovery (IPR)-to establish the ability to generate acceptable
precision and accuracy, the laboratory shall perform the following operations:
9.2.2.1 Determine the concentration of HEM and/or SGT-HEM in 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
recovery (X) and the standard deviation of the percent recovery (s) for HEM
and for SGT-HEM (if determined). 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. Use the following
equation for calculation of the standard deviation of the percent recovery:
;. (I»2
n
n-1
Equation 1
where:
n = Number of samples
x = % recovery 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 acceptable and analysis of samples may begin. If, however, s
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Method 1664. Revision B
exceeds the precision limit or X falls outside the range for recovery, system
performance is unacceptable. In this event, correct the problem and repeat
the test.
9.2.3 Equivalency demonstration for application of a method modification to compliance
monitoring - To establish the ability of a modification of this method to recover an
amount of HEM and/or SGT-HEM equivalent to the amount recovered by this method
from a specific discharge/waste stream (matrix types), proceed as follows:
NOTE: Equivalency demonstration for specific discharge/waste stream types is not required for the
modifications listed as acceptable in Section 1.7.1. For modifications not listed as acceptable at Section
1.7.1, the demonstration is needed only for an example of the specific discharge/waste stream (matrix
type) to be analyzed up to a maximum of the 9 matrix types identified below which would be required to
validate the modified method for use with all samples. If validating the modified method for use with all
samples, each example waste stream below (except POTW effluent) should be known or suspected to
contain an average concentration of 5 to 1,000 mg/L of HEM and/or SGT-HEM to be included in the
demonstration:
1. One POTW effluent
2. A second POTW effluent from a different source
3. Saline water
4. Two representative examples of different treated or untreated wastewaters likely to contain
petroleum-based substances (hydrocarbons similar in chemical composition to n-hexadecane) at
significantly different concentrations
5. Two representative examples of different treated or untreated wastewaters likely to contain
animal-based substances (animal fats similar in chemical composition to stearic acid) at
significantly different concentrations
6. Two representative examples of different treated or untreated wastewaters likely to contain
other hexane extractable materials of various chemical composition including but not limited
to, vegetable oils, waxes, soaps, greases and other related materials
9.2.3.1 Collect, extract, concentrate, and weigh the HEM or SGT-HEM in two sets
of four aliquots of unspiked wastewater. One set of four wastewater aliquots
is analyzed according to the protocol in Section 11 of this method and the
other set of four aliquots is analyzed using the modified method.
9.2.3.2 Calculate the average concentration of HEM and SGT-HEM for the set of
results from this method and for the set of results from the modified method.
The average concentration using the modified method must be 78 to 114
percent of the average concentration produced by this method for HEM and
64 to 132 percent of the average concentration 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 and the average
concentration of the four results produced using the modified method are below the minimum level
(Section 1.6), and if the equivalency test of the modified method is passed for spikes of reference
standards into reagent water (Section 9.2.2), the modified method is deemed to be equivalent to this
method for determining HEM and or SGT-HEM on that specific discharge/waste stream.
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Method 1664. Revision B
9.3 Matrix spikes-The laboratory must spike a minimum of 5 percent of all samples from a given
sampling site or, if for compliance monitoring, from a given discharge/waste stream (matrix
type). The sample aliquot shall be spiked with the hexadecane/stearic acid spiking solution
(Section 7.10). A duplicate matrix spike (MSB) is recommended, but not required.
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-HEM in
the sample is being checked against a regulatory concentration limit, the
spiking level shall be at that limit, at 1 to 5 times the background
concentration of the sample (determined in Section 9.3.2), or at the
concentration of the OPR (Section 9.6), whichever concentration is highest.
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
recovery standard (Section 7.11) or at 1 to 5 times higher than the
background concentration, whichever concentration is higher.
9.3.2 Analyze one sample aliquot out of each set of 20 samples from each site or
discharge/waste stream according to the procedure beginning in Section 11 to
determine the background concentration (B) of HEM or SGT-HEM.
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).
NOTE: Samples containing high concentrations (> 100 mg/L) of HEM will require a large
volume of spiking solution (Section 7.10) for the MS (and MSB). If the concentration of HEM is
expected to exceed 1000 mg/L, smaller sample volumes should be collected for the background
measurement and MS (and MSB) so that the amount of HEM plus the amount spiked does not
exceed 1000 mg/L.
9.3.2.2 Spike the additional sample aliquot(s) with the spiking solution and analyze
the aliquot(s) 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:
p= IQO(A-B)
T
Equation 2
where:
A = Measured concentration of the analyte after spiking
B = Measured background concentration of HEM or SGT HEM
T = True concentration of the spiked sample
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Method 1664. Revision B
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.
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
analytical batch is within the acceptance criteria in Table 1, an interference is
present. In this case, the result may not be reported or used for regulatory
compliance purposes and the laboratory must assess the potential cause for
the interference. If the interference is attributable to sampling, the site or
discharge/waste stream should be resampled. If the interference is
attributable to a matrix problem, the laboratory must modify the method,
repeat the tests required in Section 9.1.2, and repeat the analysis of the
sample and the MS (and MSB, if performed). Most matrix interference
problems are attributable to the formation of emulsions in the extraction.
Section 11.3.5 provides suggestions for overcoming emulsion problems.
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
batch reanalyzed. All samples must be associated with a valid MS (and
MSB, if performed).
9.3.5 If an MSB was analyzed, compute the relative percent difference (RPB) between the
MS and MSB (not between the two recoveries) using the following equation:
D, -D7
RPD = —1—-A- x 100
2
Equation 3
where:
D] = Concentration of HEM or SGTHEMin the sample
D2 = Concentration of HEM or SGTHEMin the second (duplicate) sample
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
reanalyzed.
9.3.7 As part of the QC program for the laboratory, it is suggested that method precision and
accuracy for samples be assessed and records 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 (Pa) and the standard deviation of the percent recovery (sp).
Express the accuracy assessment as a percent recovery interval from Pa - 2sp to Pa +
2sp. For example, if Pa = 90% and sp = 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).
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Method 1664. Revision B
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 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
eliminated and a blank shows no evidence of contamination. All samples must be
associated with an uncontaminated method blank before the results may be reported for
regulatory compliance purposes.
9.5 Calibration verification-Verify calibration of the balance per Section 10 before and after each
analytical batch. If calibration is not verified before and after each day or after measurement of
the analytical batch, 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 laboratory
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 recovery with the limits for ongoing precision and recovery in Table 1. If
the recovery is in the range specified, the extraction, distillation, and weighing
processes are in control and analysis of blanks and samples may proceed. If, however,
the recovery 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 the percent recovery (sr). Express the accuracy as a recovery
interval from R - 2sr to R + 2sr. 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 QCS 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. The QCS should be
analyzed monthly by laboratories performing routine analyses and less frequently by laboratories
performing these analyses intermittently.
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 spike (MS, Section 9.3), and ongoing
precision and recovery (OPR, Section 9.6) should be identical, so that the most precise results
will be obtained.
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9.9 Depending upon specific program requirements, field replicates and field spikes of the analytes of
interest 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 2 mg and 1000 mg, using class "S" or ASTM E 617-1997
Class 1 weights. It is recommended that the balance should also be calibrated with an additional
class "S" or ASTM E 617-1997 Class 1 weight that will bracket the final expected weighing
value.
10.2 Calibration shall be within ± 10% (i.e. ± 0.2 mg) at 2 mg, ± 0.5% (i.e., ± 5 mg) at 1000 mg, and if
applicable, at the appropriate user-specified tolerance for Class 1 weights greater than 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
adherence to all details.
NOTE: The procedure below is based on the preparation, extraction, and analysis of a 1-L sample. If a
smaller volume is collected for analysis, the laboratory should dilute the sample to 1 L with reagent water
so that results across the IPR, blank, OPR, MS, and, if performed, the MSB, are consistent. It is also
important that all glassware surfaces be rinsed with n-hexane to effect a quantitative transfer of the
constituents in the sample and of the hexadecane/stearic acid in the IPR, OPR, MS, and, if performed, the
MSD.
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 bottle at the water meniscus or weigh the bottle for later
determination of sample volume. Weighing will be more accurate. Mark or weigh the
MS (and MSD).
11.2 pH verification
11.2.1 Verify that the pH of the sample is less than 2 using the following procedure:
11.2.1.1 Dip a glass stirring rod into the well mixed sample.
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11.2.1.2 Withdraw the stirring rod and allow a drop of the sample to fall on or touch
the pH paper.
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 5-6 mL of HC1 or H2SO4 solution (Section 7.2) to the
1-L sample. If the sample is at high pH, use a proportionately larger amount of HC1 or
H2SO4 solution. If a smaller sample volume was collected, use a proportionately
smaller amount of HC1 or H2SO4 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 or H2SO4 solution to the blank, OPR, MS (and
MSB) to adjust the pH of these solutions to <2.
NOTE: The procedure detailed below is for separatory funnel liquid-liquid extraction. Solid-phase
extraction (SPE) may be used at the discretion of the discharger/generator and its laboratory. However, if
SPE is used, it is the responsibility of the discharger/generator and laboratory to assure that results
produced are equivalent to results produced by the procedure below. However, it should be noted that
due to the nature of some discharge/waste streams, not all samples may be amenable to analysis with a
modified method (e.g., SPE as the modification) and for these samples, 1664B should be applied as
written.
11.3 Extraction
11.3.1 Tare a clean 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 a desiccator to cool to
room temperature.
11.3.1.3 When cool, remove from the desiccator with tongs 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 of 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.
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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
minutes. If an emulsion forms between the phases and the emulsion is greater than
one-third the volume of the solvent layer, the laboratory must employ emulsion-
breaking 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 methods. Alternatively, solid-phase extraction (SPE),
continuous liquid-liquid extraction, or other extraction techniques may be used 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 dissolution or
clumping of the sodium sulfate in the extract drying process.
NOTE: The specific properties of a sample may necessitate the use of larger amounts of Na2SO4.
11.3.7 Place a filter paper (Section 6.5.2) in a filter funnel (Section 6.5.1), add approximately
10 g of anhydrous Na2SO4, and rinse with a small portion of n-hexane. Discard the
rinsate.
11.3.8 Drain the n-hexane layer (upper layer) from the separatory funnel through the Na2SO4
into the pre-weighed boiling flask containing the boiling chips (Section 11.3.1.3).
NOTE: It is important that water be removed in this step. Water allowed to filter through the Na2SO4
will dissolve some of the Na2SO4 and carry it into the boiling flask compromising the determination.
11.3.9 Repeat the extraction (Sections 11.3.3-11.3.6 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 rinsings in the flask.
NOTE: For samples that are expected to contain a high concentration of salt (e.g., waters from oil
production facilities), it may be prudent to collect the extract in a 250-mL separatory funnel and back-
extract with reagent water. After back-extraction, the extract should be drained through Na2SO4 to
remove all traces of water.
11.3.11 A milky extract indicates the presence of water. If the extract is milky, allow the
solution to stand for up to one hour to allow the water to settle. Decant the solvent
layer (upper layer) through sodium sulfate to remove any excess water as in Sections
11.3.7 and 11.3.8. Rinse the glassware and sodium sulfate with small portions of n-
hexane to effect a quantitative transfer.
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Method 1664. Revision B
11.3.12 If only SGT-HEM is to be determined, proceed to Section 11.5.
11.4 Solvent distillation
11.4.1 Connect the boiling flask to the distilling head apparatus and distill the solvent by
immersing the lower half of the flask in a water bath or a steam bath. Adjust the water
temperature as appropriate to complete the concentration. The solvent may be
collected for reuse provided the laboratory can demonstrate the solvent meets or
exceeds the purity specifications set forth in Section 7.3.
11.4.2 When the temperature in the distilling head reaches approximately 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.
11.4.2.1 Using tongs, immediately remove the flask from the heat source while it still
contains approximately 2 mL of residual liquid. Wipe the outside surface dry
to remove moisture and fingerprints and place the flask in a hood until visible
dryness is achieved while cooling at room temperature.
11.4.2.2 If desired, the flask may be placed in an oven capable of maintaining a user
defined temperature within ± 2 °C (up to 70 °C max.) for a user defined
period of time (up to 45 minutes max.).
NOTE: The laboratory should carefully monitor the flask during the final stages of distillation to assure
that all of the solvent is removed and to prevent loss of the more volatile sample constituents. Best results
are achieved when the flask is removed from the heat source while it still contains a few mL of residual
liquid and visible dryness is achieved while cooling the flask at room temperature.
11.4.3 Inspect the residue in the boiling flask for crystals. Crystal formation is an indication
that sodium sulfate may have dissolved and passed into the boiling flask. This may
happen if the drying capacity of the sodium sulfate is exceeded or if the sample is not
adjusted to low pH. If crystals are observed, redissolve the extract in n-hexane,
quantitatively transfer through a filter into another tared boiling flask, and repeat the
distillation procedure (Sections 11.4.1-11.4.2).
11.4.4 Continue to dry and cool the flask to room temperature in a desiccator for 30 minutes
minimum. Remove with tongs and weigh immediately. While at room temperature and
without additional heating, repeat the cycle of desiccating and weighing until the
weight loss of the flask and dried residue is less than 4 % of the previous weight or less
than 0.5 mg, whichever is less. The final weighing should be used for determining the
value for HEM or SGT-HEM as appropriate.
11.4.4.1 If the extract was from the HEM procedure, determine the HEM (Wh) by
subtracting 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 (Ws) by subtracting the tare weight from the total
weight of the flask.
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Method 1664. Revision B
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
determine Vs by difference, assuming a sample density of 1.00.
11.5 SGT-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 less than 100 mg or, if above 100 mg, must be known.
11.5.1.1 If it is known that the amount of HEM is less than 100 mg, the laboratory
may proceed with the determination of SGT-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 normally adsorb 100 mg of all adsorbable
materials. Therefore, for samples containing 1000 mg HEM, 30 g of silica gel will be
needed. 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. If the amount of HEM in the sample is greater
than 1000 mg, 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
necessary, warm the solution to completely redissolve the HEM.
11.5.2.2 Quantitatively transfer the extract to a 100-mL volumetric flask. Dilute to
the mark with n-hexane.
11.5.2.3 Calculate the extract volume that contains 1000 mg of extractable material
according to the following equation:
V = 1000Vt
Equation 4
where:
Va = Volume of the aliquot to be withdrawn (mL)
Vt = Total volume of solvent used in Section 11.5.2.2 (mL)
Wh = Weight of extractable material from the 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.
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Method 1664. Revision B
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 fluoropolymer-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 Distill 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:
VS(L)
Equation 5
where:
Wh = Weight of extractable material from Section 11.4.4.1 (mg)
Vs = Sample volume from Section 11.4.5 (L)
12.2 Silica gel treated n-hexane extractable material-calculate the concentration of SGT-HEM ("non-
polar material") in the sample per the equation above, substituting Ws (from Section 11.4.4.2) for
Wh. If the extract was split to decrease the total amount of material to 1,000 mg, determine the
corrected total weight of SGT-HEM in the unsplit extract (Wc) using the following equation:
Equation 6
where:
Wc = Corrected total weight of SGT-HEM in the unsplit extract
Wd = Weight in the portion of the extract split for adsorption (Sections 11.5.2.4 and 11.4.4.2)
Va = Volume of aliquot withdrawn (mL)
Vt = Total volume of solvent used in Section 11.5.2.2 (mL)
Use the corrected total weight of SGT-HEM in the unsplit extract (Wc) to determine the total
SGT-HEM in the sample by substituting Wc for Wh in Equation 5.
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Method 1664. Revision B
12.3 Reporting-Report results to three significant figures for HEM and SGT-HEM found at or above
10 mg/L, and report results to two significant figures for HEM and SGT-HEM found below 10
mg/L.
12.3.1 Samples-Report results for HEM and SGT-HEM found below the ML as < 5.0 mg/L,
or as required by the permitting authority or permit.
12.3.2 Blanks-Report results for HEM and SGT-HEM found below the MDL as less than the
actual MDL value, i.e., < 1.4 mg/L, or as required by the permitting authority or permit.
Do not report results below the MDL unless required by the permitting authority or
permit.
12.3.3 Results from tests performed with an analytical system that is not in control (Section 9)
must not be reported or otherwise used for permitting or regulatory compliance
purposes and do not relieve a discharger or permittee of timely reporting.
13.0 Method Performance
13.1 This method was validated through single-laboratory studies and an inter-laboratory method
validation study (Reference 16.9). Combined data from these studies show an average recovery
of 93 percent for HEM and 89 percent for SGT-HEM and precision (as relative standard
deviation) of 8.7 percent for HEM and 13 percent for SGT-HEM.
13.2 The method detection limit (MDL) and minimum level of quantitation (ML) are based on five
studies conducted by EPA and described at proposal of Method 1664 (61 FR 1730) and as
verified by data submitted in comments on the proposal of Method 1664 (Reference 16.3).
14.0 Pollution Prevention
14.1 The solvents used in this method pose little threat to the environment when recycled and managed
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
governing 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 HC1 or H2SO4 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. Revision B
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 NW, Washington, DC 20036.
16.0 References
16.1 "Methods for Chemical Analysis of Water and Wastes," 3rd Edition, Environmental Protection
Agency, Environmental Monitoring Systems Laboratory-Cincinnati (EMSL-Ci), Cincinnati, Ohio
45268, EPA-600/4-79-020, Method 413.1, (1983).
16.2 "Methods for Chemical Analysis of Water and Wastes," 3rd Edition, Environmental Protection
Agency, Environmental Monitoring Systems Laboratory-Cincinnati (EMSL-Ci), Cincinnati, Ohio
45268, EPA-600/4-79-020, Method 418.2
16.3 Guidelines Establishing Test Procedures for the Analysis of Oil and Grease and Non-polar
Materials; Final Rule; Preamble, Responses to Comments, and Docket, as referenced in the Final
Rule, March 7, 2007; 72 FR 11199.
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 "Report on the Method 1664 Validation Studies," April 1995. Available from the CWA Methods
Team, OSTCWAMethods@epa.gov.
16.10 "Analytical Method Guidance for EPA Method 1664A Implementation and Use (40 CFR part
136)," USEPA Office of Water, EPA/82 l-R-00-003, February 2000.
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Method 1664. Revision B
17.0 Tables
Table 1. Acceptance Criteria for Performance Tests
Acceptance Criterion
Initial precision and recovery
HEM Precision (s)
HEM Recovery (X)
SGT-HEM Precision (s)
SGT-HEM Recovery (X)
Matrix spike/matrix spike duplicate
HEM Recovery
HEMRPD
SGT-HEM Recovery
SGT-HEM RPD
Ongoing precision and recovery
HEM Recovery
SGT-HEM Recovery
Section
9.2.2
9.2.2.2
9.2.2.2
9.2.2.2
9.2.2.2
9.3
9.3.4
9.3.5
9.3.4
9.3.5
9.6
9.6
9.6
Limit (%)
11
83 -101
28
83-116
78-114
18
64-132
34
78-114
64-132
18.0 Glossary of Definitions and Purposes
The definitions and purposes are specific to this method but have been conformed to common
usage to the extent 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
mg/L milligram per liter
mg/mL milligram per milliliter
mL milliliter
No. number
rpm revolutions per minute
18.2 Definitions, acronyms, and abbreviations
18.2.1 Analyte-The HEM or SGT-HEM determined by this method.
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Method 1664. Revision B
18.2.2 Analytical batch-The set of samples started through the extraction process in a 12-hour
shift, to a maximum of 20 field samples. Each analytical batch of 20 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, (Section 9.3), resulting in a
minimum of four analyses (1 sample, 1 blank, 1 OPR, and 1 MS) and a maximum of 23
analyses (20 field samples, 1 blank, 1 OPR, and 1 MS) in the batch. If greater than 20
samples are to be extracted in a 12-hour shift, the samples must be separated into
analytical batches of 20 or fewer samples.
18.2.3 Discharge (matrix type)-A sample medium with common characteristics across a given
industrial subcategory (40 CFR parts 403-500). For example, C-stage effluents from
chlorine bleach mills in the Pulp, Paper, and Paperboard industrial category; effluent
from the Continuous Casting subcategory of the Iron and Steel industrial category;
publicly owned treatment work (POTW) sludge; and in-process streams in the Atlantic
and Gulf Coast Hand-shucked Oyster Processing subcategory are each a matrix type.
18.2.4 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
purpose of the field blank is to determine if the field or sample transporting procedures
and environments have contaminated the sample.
18.2.5 HEM-See n-Hexane extractable material.
18.2.6 n-Hexane extractable material-Material that is extracted from a sample using the
extraction solvent n-hexane and gravimetrically determined by this method, otherwise
known by the common name "oil and grease". This material includes relatively non-
volatile hydrocarbons, vegetable oils, animal fats, waxes, soaps, greases, and related
matter.
18.2.7 IPR-See initial precision and recovery.
18.2.8 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 is modified.
18.2.9 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.
18.2.10 Laboratory control sample (LCS)-See Ongoing precision and recovery standard (OPR).
18.2.11 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 MSB 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
background concentrations of the analytes in the sample matrix must be determined in
a separate aliquot and the measured values in the MS and MSB corrected for
background concentrations.
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Method 1664. Revision B
18.2.12 May-This action, activity, or procedural step is neither required nor prohibited.
18.2.13 May not-This action, activity, or procedural step is prohibited.
18.2.14 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.
18.2.15 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.
18.2.16 Must-This action, activity, or procedural step is required.
18.2.17 Ongoing precision and recovery standard (OPR, also called a laboratory control
sample)-A laboratory blank spiked with known quantities 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.
18.2.18 OPR-See ongoing precision and recovery standard.
18.2.19 PAR-See precision and recovery standard.
18.2.20 Precision and recovery standard-Secondary standard that is diluted and spiked to form
the IPR and OPR.
18.2.21 Quality control sample (QCS)-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.
18.2.22 Quantitative transfer-The process of transferring a solution from one container to
another using a pipet in which as much solution as possible is transferred, followed by
rinsing of the walls of the source container with a small volume of rinsing solution
(e.g., n-hexane), followed by transfer of the rinsing solution, followed by a second and
third rinse and transfer.
18.2.23 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.
18.2.24 Regulatory Compliance Limit-A limit on the concentration or amount of a pollutant or
contaminant specified in a nationwide standard, in a permit, or otherwise established by
a regulatory authority.
18.2.25 SGT-HEM-See Silica gel treated n-hexane extractable material.
18.2.26 Should-This action, activity, or procedural step is suggested but not required.
18.2.27 Silica gel treated n-hexane extractable material-Components of n-Hexane extractable
material (HEM) that are not adsorbed by silica gel and are gravimetrically determined
by this method, otherwise known as non-polar material (NPM).
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Method 1664. Revision B
18.2.28 SPE-Solid-phase extraction is an extraction technique in which the analytes of interest
that may be present in a sample are selectively adsorbed onto a disk or cartridge, and
subsequently desorbed by an eluting solvent.
18.2.29 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.
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