Oil & Grease by EPA Method 1664

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. 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. 2. 11.2—pH verification.

  3. 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.
    3. NOTE: Do not dip the pH paper into the bottle or touch it to the sample on the lid.
    4.—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.

    1. 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.

    2. 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.

    3. 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.

  4. 3. 11.3—Extraction

    1. 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. 2. 11.3.2—Pour the sample into the separatory funnel.

    3. 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. 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. 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. 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.

    7. 7. 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.

    8. 8. 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.

    9. 9. 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.

    10. 10. 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. 11. 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.

    12. 12. 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.

    13. 13. 11.3.12—If only SGT-HEM is to be determined, proceed to Section 11.5.

  5. 4. 11.4—Solvent distillation.

    1. 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. 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. 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. 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. 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.

  6. 5. 11.5—SGT-HEM determination.

    1. 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. 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:

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      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. 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. 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. 5. 11.5.5—Distill the solution and determine the weight of SGT-HEM per Section 11.4.