Composition-selective detection of polychlorinated biphenyls (PCBs) by oxygen-chlorine exchange reaction in a tandem mass spectrometer (MS/MS).

The exchange reaction of chlorine by oxygen with polychlorinated biphenyl (PCB) anions was explored as a method for composition-selective detection of PCB congeners in a gas chromatograph/tandem mass spectrometer (GC/MS/MS) experiment. The odd-electron molecular anions of PCBs react with molecular oxygen introduced into the collision cell of a triple-quadrupole mass spectrometer to form a product ion that has 19 mass units less (35Cl - 16O) than the precursor. The even-electron anions which also form in the source do not react when allowed to pass through the precursor analyzer. Multiple reaction monitoring allows the generation of separate chromatograms for each different composition from tetrachloro through nonochloro PCB. Most coelutants are resolved in this way. Response factors for the 12 coplanar congeners that exhibit dioxin-like toxicity relative to octachloronaphthalene vary from 1.6 to 580. Results of the analysis of an Aroclor 1242 sample for the coplanar congeners compare well with previously determined values.