Enantioselective gas chromatography mass spectrometry of methylsulfonyl PCBs with application to arctic marine mammals

Four different commercially available cyclodextrin (CD) capillary gas chromatography (GC) columns were tested for the enantioselective separation of nine environmentally persistent atropisomeric 3- and 4-methylsulfonyl PCBs (MeSO2-CBs), The selected columns contained cyclodextrins with various cavity diameters (beta- or gamma-CD), which were methylated and/or tert-butyldimethylsilylated (TBDMS) in the 2,3,6-O-positions. The beta-CD column with TBDMS substituents in all of the 2,3,6-O-positions was by far the most selective column for the MeSO2-CBs tested. Enantiomers of congeners with 3-MeSO2 substitution were more easily separated than those with 4-MeSO2 substitution. The separation also seemed to be enhanced for congeners with the chlorine atoms on the non-MeSO2-containing ring and clustered on one side of the same ring. The 2,3-di-O-methyl-6-O-TBDMS-beta-CD was found to give somewhat better selectivity than the corresponding gamma-CD, in comparison between the two columns, which were identical in all other respects. Enantioselective analysis of arctic ringed seal (Phoca hispida) and polar bear (Ursus maritimus) adipose tissue revealed a strong dominance of certain enantiomers, For example, the enantiomer ratio (ER) of 3-MeSO2-CB149 was 0.32 and <0.1 in ringed seal blubber and polar bear fat, respectively. These low ER values are indicative of highly enantioselective formation, enantioselective metabolism, enantioselective transport across cell membranes, or a combination of the three in both species. Comparable results for the enantiomeric analysis of MeSO2-CBs in biotic tissue extracts were obtained using two highly selective mass spectrometric techniques, ion trap mass spectrometry/mass spectrometry and electron capture negative ion low-resolution mass spectrometry.