A procedure involving column chromatography and preparative thin-layer chromatography, with high-resolution mass spectrometry, has been developed for the determination of polycyclic aromatic hydrocarbons in mineral oils. The approximate content of these hydrocarbons can be determined by preparative thin-layer chromatography and a more accurate result obtained by analysing certain fractions from this separation by mass spectrometry. The mono-and dicyclic aromatic hydrocarbon contents can also be determined from the analysis of these fractions and considerable additional information is obtained about the types of polycyclic aromatic hydrocarbons present, as designated by Z number in the hydrocarbon formula C_nH_2n+z.

Limitations of the procedure result from the presence of sulphur compounds in the thin-layer chromatographic fractions, although assumptions can be made that permit certain of these compounds to be determined in the mass-spectrometric analysis. Also, the latter method is not applicable to oils containing appreciable amounts of compounds with relative molecular masses higher than 500.