Introduction

Several analytical techniques measure the amount of oil and grease in water. These techniques may be broadly classified as either gravimetric or infrared (IR) absorbance methods and are described in detail here. These methods are based on the extraction of oil and grease into a solvent. A sample may contain suspended solids, which have to be filtered. In this case, the sample must first undergo solvent extraction followed by filtration of the extract.

Several different solvents have been used. These include petroleum ether, diethyl ether, chloroform, and carbon tetrachloride. Of these, petroleum ether and diethyl ether are highly flammable, whereas chloroform (although a very good solvent) and carbon tetrachloride are toxic. Thus, these solvents are not recommended for use. Currently, 1,1,2-trichloro, trifluoroethane (Freon 113) is used when infrared (IR) absorbance is used for analysis. However, these solvents are being phased out because of potential interference with the ozone layer in the atmosphere. Studies are currently under way to find a replacement solvent. Potential candidates include hexane, cyclohexane, methylene chloride, perchloroethylene, and a commercial hydrochlorofluorocarbon (DuPont 123). When the gravimetric technique is used for analysis, 1, 1, 1-trichloroethane or dichloroethylene may also be used.

"Total oil and grease" is defined by the measurement procedure stipulated by the authorities having jurisdiction. Important variations that could give different results for the same sample are

• Number of extractions performed on the water sample. Multiple extractions with Freon on the same water sample will generally give a higher oil concentration than a single...