Applicable to the quantitative determination of contents of benzene, C8 aromatics and aliphatics up to n-nonane in the range between 0.01 % (m/m) and 1.00 % (m/m). Alternatives that will give equivalent results may also be used. Addition of a known amount of intgernal standard to a test portion and introduction of an aliquot portion of this mixture into a separating column. Sweeping of the vaporized mixture through the column by a flow of carrier gas. Detection of each component as it emerges by a flame ionization detector and recording as a peak on a diagram. Identification by their relative retention times and quantitative determination from the ratio of their peak areas.