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Water: Petrochemicals-Oils

Analytical Methods - Method 1664, Revision A: 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

EPA-821-R-98-002; February 1999

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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 non-polar material.

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.

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1.0 Scope and Application

  1. 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).
  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 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).
  3. 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.
  4. 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.
  5. 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.
  6. 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).
  7. 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.
  8. 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.
  9. 1.9—Each laboratory that uses this method must demonstrate the ability to generate acceptable results using the procedure in Section 9.2.

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2.0 Summary of Method

  1. 2.1—A 1-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. 2.2—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.
  3. 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.
  4. 2.4—Quality is assured through calibration and testing of the extraction, distillation, and gravimetric systems.

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3.0 Definitions

  1. 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. 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.
  2. 3.2—Definitions for terms used in this method are given in the glossary at the end of the method.

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4.0 Interferences

  1. 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.
  2. 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.
  3. 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. 4.4—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.
  5. 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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5.0 Safety

  1. 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.
  2. 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.
  3. 5.3—n-Hexane has a flash point of -23 C (-9 F), has explosive limits in air in the range of 1 - 7 percent, 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.
  4. 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. 5.5—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.

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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.

  1. 6.1—Sampling equipment.
    1. 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), a smaller sample container may be used.

    2. 6.1.2—Cleaning.
      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.
      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.
    3. 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.
  2. 6.2—Equipment for glassware cleaning.
    1. 6.2.1—Laboratory sink with overhead fume hood.
    2. 6.2.2—Oven--Capable of maintaining a temperature within ± 2C in the range of 70-250C.
  3. 6.3—Equipment for calibration.
    1. 6.3.1—Analytical Balance--Capable of weighing 0.1 mg.
    2. 6.3.2—Volumetric flask--Glass, 100-mL.
    3. 6.3.3—Vials--Assorted sizes, with PTFE-lined screw caps.
    4. 6.3.4—Volumetric pipette--Glass, 5-mL.
  4. 6.4—Equipment for sample extraction.
    1. 6.4.1—Balance (optional)--Top loading, capable of weighing 500-2000g within ± 1%
    2. 6.4.2—Glass stirring rod.
    3. 6.4.3—Separatory funnel--Glass, 2000-mL, with PTFE stopcock.
    4. 6.4.4—Funnel--Large, glass, for pouring sample into separatory funnel.
    5. 6.4.5—Centrifuge (optional)--Explosion proof, capable of spinning at least four 100-mL glass centrifuge tubes at 2400 rpm minimum.
    6. 6.4.6—Centrifuge tubes (optional)--100-mL glass.
  5. 6.5—Equipment for removal of water, sodium sulfate, and silica gel fines.
    1. 6.5.1—Funnel--Analytical, glass.
    2. 6.5.2—Filter paper--Whatman No. 40 (or equivalent), to fit funnel.
  6. 6.6—Equipment for solvent distillation.
    1. 6.6.1—Water bath or Steam bath--Explosion-proof, capable of maintaining a temperature of at least 85C.
    2. 6.6.2—Flask--Boiling, 125-mL (Corning No. 4100 or equivalent).
    3. 6.6.3—Distilling head--Claisen (VWR Scientific No. 26339-005, or equivalent), includes Claisen-type connecting tube and condenser.
    4. 6.6.4—Distilling adaptor (attached to the distilling head and to the distillate collection flask for recovery of solvent).
    5. 6.6.5—Distillate collection flask (attached to the distilling adaptor for collection of the distilled solvent).
    6. 6.6.6—Ice bath or recirculating chiller (to aid in the condensation and collection of the distilled solvent).
    7. 6.6.7—Vacuum--Vacuum pump or other source of vacuum.
    8. 6.6.8—Tongs, for handling the boiling flask (Baxter Scientific Products No. T5007-2, or equivalent).
    9. 6.6.9—Desiccator--Cabinet- or jar-type, capable of keeping the boiling flask (Section 6.6.2) dry during cooling.
    10. 6.6.10—Hood-Explosion-proof, capable of accommodating the equipment used for solvent distillation (Section 6.6.1-6.6.5).
  7. 6.7—Equipment for removal of adsorbable materials.
    1. 6.7.1—Magnetic stirrer.
    2. 6.7.2—PTFE-coated magnetic stirring bars.
    3. 6.7.3—Graduated cylinder--500-mL, capable of measuring ± 5 mL.
    4. 6.7.4—Pipettes--Assorted sizes, calibrated to within ± 0.5 percent.

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7.0 Reagents and Standards

  1. 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.
  2. 7.2—Hydrochloric acid or sulfuric acid--ACS. Mix equal volumes of concentrated HCl and reagent water or 1 part H2SO4 and 3 parts reagent water to produce an approximately 6N solution.
  3. 7.3—n-Hexane--85% minimum purity, 99.0% min. saturated C6 isomers, residue less than 1 mg/L.
  4. 7.4—Acetone--ACS, residue less than 1 mg/L.
  5. 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.

  6. 7.6—Boiling chips--Silicon carbide or fluoropolymer.
  7. 7.7—Silica gel--Anhydrous, 75 - 150 micrometers, Davisil Grade 923 (Supelco 21447-7A, or equivalent). Dry at 200-250C 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).
  8. 7.8—Hexadecane--98% minimum purity.
  9. 7.9—Stearic acid--98% minimum purity.
  10. 7.10—Hexadecane/stearic acid (1:1) spiking solution--Prepare in acetone at a concentration of 2 mg/mL each.
    1. 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.

    2. 7.10.2—After the hexadecane and stearic acid have dissolved, transfer the solution to a 100-150 mL vial with fluoropolymer-lined cap. Mark the solution level on the vial and store in the dark at room temperature.
    3. 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.

      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).

  11. 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.
  12. 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.

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8.0 Sample Collection, Preservation, and Storage

  1. 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.
    1. 8.1.1—If analysis is to be delayed for more than four hours, adjust the sample pH to less than 2 with HCl or H2SO4 solution (Section 7.2) at the time of collection, and refrigerate at 0-4C (40 CFR 136, Table II). To establish the volume of HCl 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. 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.
    2. 8.1.2—If a sample is known or suspected to contain greater than 500 mg/L 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 HCl or H2SO4 solution to the smaller sample if preservation is necessary.
  2. 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.

  3. 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).
  4. 8.4—All samples must be refrigerated at 0-4C from the time of collection until extraction (40 CFR 136, Table II).
  5. 8.5—All samples must be analyzed within 28 days of the date and time of collection (40 CFR 136, Table II).

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9.0 Quality Control

  1. 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.
    1. 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.
    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 solid-phase extraction, continuous liquid-liquid extraction, and Kuderna-Danish concentration. Alternate determinative techniques, such as infrared spectroscopy or immunoassay, 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. 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.
      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 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. The tests required for this equivalency demonstration are given in Section 9.2.3.
      2.—The laboratory is required to maintain records of modifications made to this method. These records include the following, at a minimum:
        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.
        2.—A listing of pollutant(s) measured (HEM and/or SGT-HEM).
        3.—A narrative stating reason(s) for the modification.
        4.—Results from all quality control (QC) tests comparing the modified method to this method, including:
          • Calibration (Section 10).
          • Calibration verification (Section 9.5).
          • Initial precision and recovery (Section 9.2.2).
          • Analysis of blanks (Section 9.4).
          • Accuracy assessment (Section 9.3).
          • Ongoing precision and recovery (Section 9.6).
          • Method detection limit (Section 9.2.1).
        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:
          • Sample numbers and other identifiers.
          • Extraction dates.
          • Analysis dates and times.
          • Analysis sequence/run chronology.
          • Sample weight or volume (Section 11.1.4).
          • Extract volume for SGT-HEM (Section 11.5.2).
          • Make and model of analytical balance and weights traceable to NIST.
          • Copies of logbooks, printer tapes, and other recordings of raw data.
          • Data system outputs, and other data to link the raw data to the results reported.
    3. 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.
    4. 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.
    5. 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.
    6. 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.
    7. 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.
  2. 9.2—Initial demonstration of laboratory capability.
    1. 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.
    2. 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:
      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.
      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:
        equation 1: This image is too complicated for a description. Please contact OW-GENERAL@epa.gov for more information.

      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 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.
    3. 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, proceed as follows:
      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.
      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.

  3. 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 spike). The sample aliquot shall be spiked with the hexadecane/stearic acid spiking solution (Section 7.10). A duplicate matrix spike (MSD) is recommended but not required.
    1. 9.3.1—The concentration of the spike in the sample shall be determined as follows:
      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 9.4), whichever concentration is highest.
      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.
    2. 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.
      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 (

      2. 100 mg
      3. /L) of HEM will require a large volume of spiking solution (Section 7.10) for the MS (and MSD). 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 MSD) so that the amount of HEM plus the amount spiked does not exceed 1000 mg/L.
      4.—Spike the additional sample aliquot(s) with the spiking solution and analyze the aliquot(s) to determine the concentration after spiking (A).
    3. 9.3.3—Calculate the percent recovery (P) of HEM or SGT-HEM in each aliquot using the following equation:
      equation 2: This image is too complicated for a description. Please contact OW-GENERAL@epa.gov for more information.

      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.
    4. 9.3.4—Compare the percent recovery of the HEM or SGT-HEM with the corresponding QC acceptance criteria in Table 1.
      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 purposes 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 MSD, 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.
      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 MSD, if performed).
    5. 9.3.5—If an MSD was analyzed, compute the relative percent difference (RPD) between the MS and MSD (not between the two recoveries) using the following equation:
      equation 3: This image is too complicated for a description. Please contact OW-GENERAL@epa.gov for more information.

    6. 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.
    7. 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).
  4. 9.4—Laboratory blanks--Laboratory reagent water blanks are analyzed to demonstrate freedom from contamination.
    1. 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.
    2. 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.
  5. 9.5—Calibration verification--Verify calibration of the balance per Section 10 before and after each analytical batch. If calibration is not verified after measurement of the analytical batch, recalibrate the balance and reweigh the batch.
  6. 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:
    1. 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.
    2. 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.
    3. 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%.
  7. 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.
  8. 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.
  9. 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.

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10.0 Calibration and Standardization

  1. 10.1—Calibrate the analytical balance at 2 mg and 1000 mg using class "S" weights.
  2. 10.2—Calibration shall be within ± 10% (i.e. ±0.2 mg) at 2 mg and ± 0.5% (i.e. ±5 mg) at 1000 mg. If values are not within these limits, recalibrate the balance.

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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 MSD, 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.

  1. 11.1—Preparation of the analytical batch.
    1. 11.1.1—Bring the analytical batch of samples, including the sample aliquots for the MS (and MSD), to room temperature.
    2. 11.1.1—Place approximately 1000 mL (950-1050 mL) of reagent water (Section 7.1) in a clean sample bottle to serve as the laboratory blank.
    3. 11.1.3—Prepare the OPR (Section 9.6) using the PAR standard (Section 7.11).
    4. 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).
  2. 11.2—pH verification.
    1. 11.2.1—Verify that the pH of the sample is less than 2 using the following procedure:
      1.—Dip a glass stirring rod into the well mixed sample.
      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.

      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.
    2. 11.2.2—If the sample is at neutral pH, add 5-6 mL of HCl or H2SO4 solution (Section 7.2) to the 1-L sample. If the sample is at high pH, use a proportionately larger amount of HCl or H2SO4 solution. If a smaller sample volume was collected, use a proportionately smaller amount of HCl or H2SO4 solution.
    3. 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.
    4. 11.2.4—Add the appropriate amount of HCl or H2SO4 solution to the blank, OPR, MS (and MSD) 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.

  3. 11.3—Extraction
    1. 11.3.1—Tare a clean boiling flask containing 3-5 boiling chips as follows:
      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.
      2.—Remove from the oven and immediately transfer to a desiccator to cool to room temperature.
      3.—When cool, remove from the desiccator with tongs and weigh immediately on a calibrated balance (Section 10).
    2. 11.3.2—Pour the sample into the separatory funnel.
    3. 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.
    4. 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.
    5. 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.
    6. 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 solution drying process.

    7. 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.

      NOTE: The specific properties of a sample may necessitate the use of larger amounts of Na2SO4.

    8. 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

      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.

    9. 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.
    10. 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. 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.
    12. 11.3.12—If only SGT-HEM is to be determined, proceed to Section 11.5.
  4. 11.4—Solvent distillation.
    1. 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 required to complete the concentration in less than 30 minutes. Collect the solvent for reuse.
    2. 11.4.2—When the temperature in the distilling head reaches approximately 70C 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. Using tongs, immediately remove the flask from the heat source and wipe the outside surface dry to remove moisture and fingerprints.

      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.

    3. 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).
    4. 11.4.4—Dry the boiling flask for 30 - 45 minutes in an oven maintained at 70 ± 2 C. Cool to room temperature in a desiccator and maintain in the desiccator for 30 minutes minimum. Remove with tongs and weigh immediately. Repeat the cycle of drying, cooling, desiccating, and weighing until the weight loss is less than 4 % of the previous weight or less than 0.5 mg, whichever is less.
      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.
      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.
    5. 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.
  5. 11.5—SGT-HEM determination.
    1. 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.
      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.
      2.—If, however, the amount of HEM is not known, HEM must first be determined using the procedure in Sections 11.3-11.4.
    2. 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:
      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.
      2.—Quantitatively transfer the extract to a 100-mL volumetric flask. Dilute to the mark with n-hexane.
      3.—Calculate the extract volume that contains 1000 mg of extractable material according to the following equation:
        equation 4: This image is too complicated for a description. Please contact OW-GENERAL@epa.gov for more information.

      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.
    3. 11.5.3—Adsorption with silica gel
      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.
      2.—Add a fluoropolymer-coated stirring bar to the flask and stir the solution on a magnetic stirrer for a minimum of 5 minutes.
    4. 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.
    5. 11.5.5—Distill the solution and determine the weight of SGT-HEM per Section 11.4.

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12.0 Data Analysis and Calculations

  1. 12.1—n-Hexane extractable material--Calculate the concentration of HEM ("oil and grease") in the sample per the following equation:
    equation 5: This image is too complicated for a description. Please contact OW-GENERAL@epa.gov for more information.

  2. 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 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 un-split extract (Wc) using the following equation:
    equation 6: This image is too complicated for a description. Please contact OW-GENERAL@epa.gov for more information.

    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.
  3. 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.
    1. 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.
    2. 12.3.2—Blanks--Report results for HEM and SGT-HEM found below the MDL as < 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.
    3. 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 but do not relieve a discharger or permittee of timely reporting.

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13.0 Method Performance

  1. 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.
  2. 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).

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14.0 Pollution Prevention

  1. 14.1—The solvents used in this method pose little threat to the environment when recycled and managed properly.
  2. 14.2—Standards should be prepared in volumes consistent with laboratory use to minimize the volume of expired standards to be disposed.

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15.0 Waste Management

  1. 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.
  2. 15.2—Samples preserved with HCl or H2SO4 to pH < 2 are hazardous and must be neutralized before being disposed, or must be handled as hazardous waste.
  3. 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.

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16.0 References

  1. 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).
  2. 16.2—Ibid., Method 418.1
  3. 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.
  4. 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.
  5. 16.5—"OSHA Safety and Health Standards, General Industry," (29 CFR 1910), Occupational Safety and Health Administration, OSHA 2206 (Revised, January 1976).
  6. 16.6—"Safety in Academic Chemistry Laboratories," American Chemical Society, Committee on Chemical Safety, 3rd Edition, 1979.
  7. 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.
  8. 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.
  9. 16.9Report of the Method 1664 Validation Studies, April 1995. Available from the Sample Control Center (operated by DynCorp I&ET), 6101 Stevenson Avenue, Alexandria, VA 22304, (703) 461-2100.

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17.0 Table 1. Acceptance Criteria for Performance Tests

Acceptance Criterion Section Limit (%)
Initial precision and recovery 9.2.2
HEM Precision (s) 11
HEM Recovery (X) 83-101
SGT-HEM Precision (s) 28
SGT-HEM Recovery (X) 83-116
Matrix spike/matrix spike duplicate 9.3
HEM Recovery 9.3.4 78-114
HEM RPD 9.3.5 18
SGT-HEM Recovery 9.3.4 64-132
SGT-HEM RPD 9.3.5 34
Ongoing precision and recovery 9.6
HEM Recovery 9.6 78-114
SGT-HEM Recovery 9.6 64-132

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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.

  1. 18.1—Units of weight and measure and their abbreviations
    1. 18.1.1—Symbols
      C degrees Celsius
      < less than
      % percent
      ± plus or minus
    2. 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
  2. 18.2—Definitions, acronyms, and abbreviations
    1. 18.2.1Analyte: The HEM or SGT-HEM determined by this method.
    2. 18.2.2Analytical 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.
    3. 18.2.3Discharge (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.
    4. 18.2.4Field 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.
    5. 18.2.5HEM: See n-Hexane extractable material.
    6. 18.2.6n-Hexane extractable material: Material that is extracted from a sample and determined by this method (oil and grease). This material includes relatively non-volatile hydrocarbons, vegetable oils, animal fats, waxes, soaps, greases, and related matter.
    7. 18.2.7IPR: See initial precision and recovery.
    8. 18.2.8Initial 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.
    9. 18.2.9Laboratory 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.
    10. 18.2.10Laboratory control sample (LCS): See Ongoing precision and recovery standard (OPR).
    11. 18.2.11Matrix 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 background 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.
    12. 18.2.12May: This action, activity, or procedural step is neither required nor prohibited.
    13. 18.2.13May not: This action, activity, or procedural step is prohibited.
    14. 18.2.14Method Detection Limit: The lowest level at which an analyte can be detected with 99 percent confidence that the analyte concentration is greater than zero.
    15. 18.2.15Minimum 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.
    16. 18.2.16Must: This action, activity, or procedural step is required.
    17. 18.2.17Ongoing 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. 18.2.18OPR: See ongoing precision and recovery standard.
    19. 18.2.19PAR: See precision and recovery standard.
    20. 18.2.20Precision and recovery standard: Secondary standard that is diluted and spiked to form the IPR and OPR.
    21. 18.2.21Quality 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.
    22. 18.2.22Quantitative 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.
    23. 18.2.23Reagent water: Water demonstrated to be free from HEM and SGT-HEM and potentially interfering substances at or above the minimum level of this method.
    24. 18.2.24Regulatory 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.
    25. 18.2.25SGT-HEM: See Silica gel treated n-hexane extractable material.
    26. 18.2.26Should: This action, activity, or procedural step is suggested but not required.
    27. 18.2.27Silica gel treated n-hexane extractable material: Components of n-Hexane extractable material (HEM) that are not adsorbed by silica gel; i.e., non-polar material (NPM).
    28. 18.2.28Stock 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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This method was prepared under the direction of William A. Telliard of the Engineering and Analysis Division within EPA's Office of Water. This document was prepared under EPA Contract No. 68-C-98-139 by DynCorp Information and Enterprise Technology.


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 an endorsement or recommendation for use.

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