Oil or grease may be present in
water as an emulsion from industrial waste s or similar sources, or a light petroleum fraction may be in solution. Some
Oil in natural waters may be derived from the decomposition of plankton or higher forms of aquatic life. Most heavy oils and greases are insoluble in water but may be emulsified or saponified by detergents, alkalis, or other chemicals. Low-boiling fraction are lost in ordinary oil and grease analysis, and special techniques for their determination have been developed. Even lubricating oil fractions evaporate at a significant rate at the temperature, which is necessary for removal of the last traces of the extraction solvent. Dissolved or emulsified oil or grease is extracted from water by intimate contact with various organic solvents. Some extractable, especially unsaturated fats and fatty acids oxidize readily; hence, special precautions regarding temperature and solvent vapor displacement are included to minimize this effect. Storage of the sample Stored samples should be acidified with 5
ml of 1+1 H2SO4 per liter to inhibit bacterial activity. Since many oils and hydrocarbons are utilized by bacteria, storage is obviously detrimental.
APPARATUS Separatory funnel with inert Teflon stopcock
REAGENTS 1+1 H2SO4 Petroleum ether (double distilled)
PROCEDURE 1. Place the sample, usually 1 L, in a separatory funnel of sufficient size to allow the addition of acid and solvent, and still have space for proper agitation. 2. acidify the sample with 5 ml H2SO4 per liter 3. Rinse the sample bottle carefully with 15 ml petroleum ether, and add the ether washing to the separatory funnel. And an additional 25 ml ether to the separatory funnel, shaking vigorously for 2 min. 4. Allow the ether layer to separate. Withdraw the aqueous portion of the sample into a clean container, and transfer the solvent layer into a clean,
tared distilling
flask capable of holding at least three volume of solvent. If a clear ether layer cannot be obtained, filter the solvent layer into the tared distilling flask through the funnel containing an ether-moistured Whatman No. 40 filter paper. Use as small funnel and filter paper as practical. After all the ether from the two extractions and the final rinsing is included, wash down the funnel and filter paper twice with fresh 5-ml increments of petroleum ether. 5. return the sample to the separatory funnel, rinsing the container with 15 ml ether. Add the ether washings and additional 25 ml ether to the separatory funnel, and agitate for another 2 min. 6. allow the solvent layer to separate, and discard the aqueous phase. Add the ether extraction to the tared distilling flask, and rinse the separatory funnel with 25 ml ether. Add the ether washings to the tared distilling flask. 7. Distill off all but approximately 10 ml of the ether extract by means of a water bath or an electric heating mantle, observing all necessary safety precautions and keeping the heat source at about 70°C. Disconnect the condenser and boil off the remaining solvent from the tared flask at the same temperature. Dry on a water or steam bath. 8. When dry, lay the flask on its side to facilitate the removal of solvent vapor. Introduce approximately three volumes of dry illuminating gas into the flask to displace the solvent vapor. 9. Cool in a desiccator for 30 min and weigh.
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