Oil and Grease Determination, Solvent Hazards and Waste Disposal When Using Trichlorotrifluoroethane for Extraction

A spectrophotometric and colorimetric procedure has been developed for the determination of hydrocarbons, vegetable oils, animal fats, waxes, soaps, greases, and related oily organic matter in the aqueous phase. The analytical procedure is applicable to the measurement of most light petroleum fuels, although loss of some of light fuel present during the extraction manipulations can be expected. The water sample is acidified to a low pH (less than or equal to 2) and extracted with 1,1,2-trichloro-l,2,2-trifluoroethane (Freon 113 or CFC 113). Under controlled conditions, the oil and grease are extractable into a selected organic solvent, where the intensity of yellow color is proportional to the oil and grease concentration. The color in the selected organic solvent (Freon) is measured by spectrophotometry at recommended wavelengths. The new analytical method uses a visible spectrophotometer or a filter photometer, which is available in almost any water quality laboratories. The oil and grease concentration as low as 0.1 mg/L can be quantitatively measured, provided that a quartz cell with light path length of 5 cm or longer is used. Colorimetry (instead of spectrophotometry) can also be used if a colorimeter is properly calibrated or color charts are properly developed. Selection of an appropriate organic solvent for oil and grease analysis is discussed in terms of chemist contact risk and hazardous solvent disposal. Current Standard Methods 5520B, 5520D, 5520E, and 5520G for oil and grease analysis adopt n-hexane for solvent extraction. The authors compare the selected solvent (1,1,2-trichloro-l,2,2-trifluoroethane) with n-hexane and conclude that 1,1,2-trichloro-l,2,2-trifluoroethane is much safer than n-hexane considering the safety of both the workers and the laboratory facility although 1,1,2-trichloro-l,2,2-trifluoroethane is an ozone-depleting substance (ODS). Solvent recycle and/or proper laboratory waste management will eliminate the opportunity of ODS release into the environment.