DETERMINATION OF METHYL SULFONE-SUBSTITUTED POLYCHLOROBIPHENYLS BY MASS-SPECTROMETRIC TECHNIQUES WITH APPLICATION TO ENVIRONMENTAL-SAMPLES

A novel microsynthesis method of methyl sulfone-substituted polychlorobiphenyls (MeSO2-PCBs) and their analysis by gas chromatography/mass spectrometry (GC/MS) using both electron ionization (EI) and electron-capture negative-ion ionization (ECNI) are described. The MeSO2-PCBs are synthesized via methylthio-PCBs (MeS-PCBs) prepared by gamma-irradiation of PCBs in dimethyl disulfide. In this reaction, a Cl substituent in a PCB is displaced by a methylthio (CH3S-) group with displacement preferential to chlorines on the higher chlorinated phenyl ring. Complete oxidation to the methyl sulfone is then easily effected in a subsequent step. This fast and simple synthetic pathway results in small but, for GC/MS analysis, sufficient quantities of numerous identifiable PCB metabolites. Chromatographic characteristics of these MeSO2-PCBs are described, and their mass spectrometric Properties are summarized. Marked differences are observed in both the EI and ECNI mass spectra among various MeSO2-PCB congeners which clearly allow distinction of o-MeSO2/o'-Cl substituted isomers from others. Information obtained from this assortment of synthetic MeSO2-PCBs is applied toward the analysis of grey seal samples from the Baltic Sea. Approximately 20 tetra- to heptachloro congeners are detected in adipose and liver tissue, roughly one-third the number of PCB congeners present, and the levels of MeSO2-PCBs in adipose are approximately one-tenth those of the PCBs. In comparison to the high numbers of MeSO2-PCBS generated from the technical formulations (Aroclors) by our synthesis method, this indicates a high specificity of the metabolism of PCBs by seal. Interestingly, none of the MeSO2-PCB metabolites detected in grey seal appear to be o-CH3SO2/o'-Cl substituted.