This part of ISO 9377 specifies a method for the determination of the hydrocarbon oil index in waters by means of gas chromatography. The method is suitable for surface water, waste water and water from sewage treatment plants and allows the determination of a hydrocarbon oil index in concentrations above 0,1 mg/l. The method is not applicable to the quantitative determination of the content of volatile mineral oil. However, on the basis of the peak pattern of the gas chromatogram, certain qualitative information on the composition of the mineral oil contamination can be derived. NOTE 1 For the determination of the mineral-oil content of soils and sediment, see ISO/TR 11046. NOTE 2 The mass concentration of animal and vegetable fat in the test sample should not exceed 150 mg/l, because at higher values the adsorption capacity of the clean-up column packing may not be sufficient. NOTE 3 In the case of highly polluted waste water, especially if containing a high amount of surfactants, a loss in recovery may occur.