Removing the interference of DDT and its analogs in the analysis for residues of polychlorinated biphenyls.

A micro scale procedure is described for quantitatively separating polychlorinated biphenyls (PCBs) from DDT and its analogs. DDT and TDE are initially dehydrochlorinated with ethanolic KOH to their respective olefins, DDE and TDE-olefin (1-chloro-2,2-bis (p-chlorophenyl) ethylene). The olefins are than oxidized by CrO3 in acetic acid to the more polar dichlorobenzophenone. PCB's are eluted from a micro Florisil column with petroleum ether. Typical recoveries in the ppm range (based on a 5 g sample) were is greater than 80% for Aroclors 1254 and 1260. Recoveries generally were poorer with Aroclors of lower chlorine content and decreased with decreasing quantity of Aroclor present. The DDT group was not quantitatively determined; recoveries averaged is greater than 60% for the DDT group in the ppm range (based on a 5 g sample). The procedure was successfully applied to samples of Lake Michigan chubs containing residues of PCB's and the DDT group and to extracts of human serum fortified with Aroclors and the DDT group.