ASTM D4281 Standard Test Method for Oil and Grease (Fluorocarbon Extractable Substances) by Gravimetric Determination
TEST METHOD B - SOXHLET EXTRACTION
16. Scope
16.1 This test method covers the estimation of oil and grease from 20 to 200 mg/L in water and wastewater by a gravimetric determination of fluorocarbon extractable substances from an acidified sample.
16.2 This test method should be used with waters where emulsion problems do not permit separatory funnel extraction techniques. This test method should not be used where a significant second phase of oily material is present in the sample, due to the difficulty in recovering all the oily phase for gravimetric analysis.
17. Summary of Test Method
17.1 In this test method, an acidified water sample is filtered through diatomaceous earth on filter paper. The cake is dried and extracted in a Soxhlet apparatus for 4 h with fluorocarbon solvent.
17.2 In the gravimetric portion of the procedure, the fluorocarbon solvent containing the extracted materials is evaporated and the residue is determined gravimetrically.
18. Apparatus
18.1 Buchner Funnel, porcelain, 120-mm.
18.2 Drying Oven, 103°C.
18.3 Extraction Apparatus, consisting of Soxhlet extractor, Allihn condenser, and a boiling flask.
18.3.1 Allihn Condenser, bottom standard taper joint 45/50.
18.3.2 Boiling Flask, flat bottom, standard taper joint 24/40.
18.3.3 Soxhlet Extractor, 85 mL, top standard taper joint 45/50, bottom standard taper joint 24/40.
18.4 Heating Source, capable of heating the Soxhlet apparatus to achieve 20 solvent cycles per hour. Most commercially available hot plates or heating mantles are adequate.
18.5 Hot Water Bath or Steam Bath.
18.6 Vacuum Pump, or other source of vacuum.
18.7 Desiccator.
19. Reagents and Materials
19.1 Acetone ((CH3)2CO), technical grade.
19.2 Diatomaceous Silica Filter Aid Suspension - Add a 10-g filter aid to water and dilute to 1 L.
19.3 Extraction Thimble, 33 by 94 mm cellulose.
19.4 Filter Paper, 11-cm circles.
19.5 Fluorocarbon Solvent - (1,1,2-Trichloro-1,2,2-trifluoroethane) must be shown to contain no significant residue on evaporation. Redistill if necessary.
19.6 Glass Beads, 2 to 3 mm or TFE-fluorocarbon boiling stones.
19.7 Hydrochloric Acid (HCl), sp gr 1.19. Dilute to 1 + 1 with Type IV reagent water.
19.8 Muslin Cloth Disks, 10.5 cm, unbleached and rinsed with solvent.
19.9 Sulfuric Acid (H2SO4), sp gr 1.84. Dilute to 1 + 1 with Type IV reagent water.
19.10 Desiccant, active, indicating, silica gel or equivalent.
20. Procedure
20.1 Tare a boiling flask that has been dried at 103°C in an oven for 1 h and cooled to room temperature in a desiccator. Caution - Always handle the flask with metal tongs or weighing gloves to avoid deposition of body oils.
NOTE 7 - A reagent and materials blank should be run to show that they contain no significant residue, with respect to the precision of the method at the level measured. If the blank is significant, review procedure details and eliminate source of contamination.
20.2 Mark the sample bottle at the water meniscus for later determination of sample volume.
20.3 Prepare the filtration apparatus, consisting of muslin cloth disk, overlaid with filter paper, in a Buchner funnel. Wet the paper and muslin with water and apply a vacuum to firmly seat the filter paper. Make sure the filter paper is smooth over the surface of the funnel. Pass 100 mL of filter aid suspension through the prepared filter and wash with 1 L of water. By careful addition of the wash water, the filter aid can be washed away from the edges of the filter paper. This facilitates removal of the filter paper later without spilling the filter aid.
20.4 Filter the entire acidified sample (see 7.6) through the prepared filter.
NOTE 8 - If the entire sample collected cannot be filtered through one prepared filter, the sample can be filtered and extracted in separate portions, and the individual weights combined for the final result. Release the vacuum when the entire sample has passed through the filter. Using forceps, remove the filter paper, taking care not to lose any of the filter aid. Fold the paper several times to completely enclose the filter aid. Place the folded filter in the extraction thimble.
20.5 Wipe the inside of the sample container and Buchner funnel with pieces of filter paper soaked in fluorocarbon solvent, taking care not to remove all films caused by oil and grease and to collect all solid material. Add the pieces of paper to the extraction thimble. Warning - Wear rubber gloves to prevent fluorocarbon solvent from coming in contact with skin. Alternatively, a portion of the solvent that will be used in the extraction apparatus (see 20.7) can be used to rinse the sampling bottle and cap and these washings added directly to the Soxhlet boiling flask.
20.6 Dry the thimble in an oven at 103°C for 30 min.
20.7 Fill the thimble with glass beads, and insert into the assembled Soxhlet apparatus. Add fluorocarbon solvent to the tared boiling flask containing a few glass beads or teflon boiling stones and attach to Soxhlet apparatus. Apply heat and extract at 20 cycles per hour for four hours timed from the beginning of the first cycle.
NOTE 9 - Initially the Soxhlet apparatus should be rinsed with fluorocarbon solvent to ensure its cleanliness. In addition, some sort of loose cap can be kept over the top of the condenser to keep out any dust. Great care must be taken to ensure that no glass beads spill into the extractor chamber as they can become lodged in the syphon tube.
20.8 After refluxing for 4 h, cool and remove the extraction thimble. Pour any solvent remaining in the extraction chamber into the boiling flask. The glass beads and extraction thimble can be reused as long as there are no holes in the thimble and the exterior of the thimble is free of dust.
21. Procedure, Gravimetric
21.1 See Section 13.
22. Calculation
22.1 See Section 14.
23. Precision and Bias
23.1 Six operators from four laboratories determined three concentration levels of oil and grease in reagent water, Type IV, over three days. These data were acceptable under D2777-72, which was in place at the time this test method was validated.
23.2 Recoveries of known amounts of oil and grease in a series of prepared standards were as shown in Table 2.
23.3 It should be recognized that these data may not apply to different water matrices.
