Qualitative characterization of three combustion-related standard reference materials for polycyclic aromatic sulfur heterocycles and their alkyl-substituted derivatives via normal-phase liquid chromatography and gas chromatography/mass spectrometry

The research described here provides the most comprehensive qualitative characterization of three combustion-related standard reference materials (SRMs) for polycyclic aromatic sulfur heterocycles (PASHs) and some alkyl-substituted (alkyl-) derivatives to date: SRM 1597a (coal tar), SRM 1991 (coal tar/petroleum extract), and SRM 1975 (diesel particulate extract). An analytical approach based on gas chromatography/mass spectrometry (GC/MS) is presented for the determination of three-, four-, and five-ring PASH isomers and three- and four-ring alkyl-PASHs in the three SRM samples. The benefit of using a normal-phase liquid chromatography (NPLC) fractionation procedure prior to GC/MS analysis was demonstrated for multiple isomeric PASH groups. Using a semi-preparative aminopropyl (NH2) LC column, the three combustion-related samples were fractionated based on the number of aromatic carbon atoms. The NPLC-GC/MS method presented here allowed for the following identification breakdown: SRM 1597a - 35 PASHs and 59 alkyl-PASHs; SRM 1991-31 PASHs and 58 alkyl-PASHs; and SRM 1975-13 PASHs and 25 alkyl-PASHs. These identifications were based on NPLC retention data, the GC retention times of reference standards, and the predominant molecular ion peak in the mass spectrum. Prior to this study, only 11, 1, and 0 PASHs/alkyl-PASHs had been identified in SRM 1597a, SRM 1991, and SRM 1975, respectively.