Determination of Diesel Fuel and Motor Oil in Water and Wastes by a Modified Diesel-Range Organics Total Petroleum Hydrocarbon Method

Abstract

The American Petroleum Institute method for determination of diesel-range total petroleum hydrocarbon (TPH) by gas-liquid chromatography with flame ionization detection was modified to allow simultaneous determination of motor oil. Motor oil elutes as a broad hump of unresolved alkanes and can be distinguished readily from diesel fuel and other fuel oils by its profile. The boiling point ranges for No. 2 diesel fuel and motor oil are C10-C21 and C21-C38, respectively, and these ranges define TPHs in diesel fuel (TPH-D) and motor oil (TPH-M). By this convention, less than 6% of No. 2 diesel is characterized as TPH-M, and less than 9% of motor oil is quantitated as TPH-D. Inlet discrimination was observed when motor oil was injected with a splitless injector. Accurate motor oil quantitation with splitless sample introduction requires calibration with the product or triacontane, which has a similar response factor. Detector response to motor oil (and other petroleum products) and a homologous series of n-alkanes was nearly constant when on-column injection was used. Instrument detection limit for motor oil was about 0.5 μg (splitless injection, total area under the curve), and the widest linear range (up to 100 μg) was obtained by subtracting the solvent chromatogram. Procedures for isolation of motor oil from oil-in-water (O/W) and water-in-oil (W/O) emulsions are described. Method detection limits for diesel fuel and motor oil in purified water were 0.041 and 1.5 mg/L, respectively.