Identification and quantification of methylated PAHs in sediment by two-dimensional gas chromatography/mass spectrometry

Alkylated polycyclic aromatic hydrocarbons (alkyl-PAHs) are ubiquitously present in the environment and they are recognized as a toxicologically hazardous group. The biggest obstacle in the assessment of environmental risks of alkyl-PAHs is identification and quantification; the complete (chromatographic) separation of alkylated homologues is difficult if not impossible. Therefore, alkyl-PAHs are usually identified as a group of isomers with the same degree of alkylation and quantified as one group using one chromatographic response factor. In this study we demonstrate that the relative response factors of twenty-three methylated PAHs with the same molecular weight of 242 (six methyl-chrysenes, twelve benz[a]anthracenes and five benzo[c]phenanthrenes) range from 0.1 for 12-methylbenz[a]anthracene and 4-methylbenzo[c]phenanthrene to 1.7 for 6-methylbenz[a]anthracene. Quantification of methylated PAHs with equal molecular weights as a group using the same relative response factor can thus overestimate or underestimate their concentrations and, therefore, the toxicological risk of an environmental sample. A two-dimensional gas chromatography method was developed with which fourteen methylated PAHs (Mw = 242) could be separated. Twelve of them were identified and quantified in Elbe River sediment.