ANALYSIS OF POLYCHLORINATED-BIPHENYLS BY QUADRUPOLE ION-TRAP MASS-SPECTROMETRY .2. COMPARISON OF MASS-SPECTROMETRIC DETECTION USING ELECTRON-IMPACT AND SELECTED-ION CHEMICAL-IONIZATION WITH ELECTRON-CAPTURE DETECTION

The responses of selected-ion monitoring of electron impact mass spectra and selected-reagent-ion chemical ionization mass spectra of polychlorinated biphenyls (PCBs), relative to that of congener 153, have been determined for some 60 PCBs contained in four standard mixtures. The PCB congeners examined cover a wide range of toxicities. Average responses have been determined for PCBs as a function of both the total number of chlorine substituents and the number of ortho-substituents. Average relative responses and relative responses of individual congeners have been compared with Literature values of relative responses obtained by electron-capture detection. Detection limits for electron ionization and C2H5+ chemical ionization mass spectrometry, determined as the mass of congener 153 injected on column and yielding a signal-to-noise ratio of 5:1 were 0.76 pg and 30 pg, respectively, compared to some 70 fg for electron-capture detection. An initial exploration and evaluation have been carried out, of the potential value of using a toxicity index to define the total toxicity of a sample; such an index is based on 39 non- and mono-ortho substituted PCBs. Electron ionization, when combined with selected-ion monitoring of both molecular and fragment ions, is the more sensitive mass-selective method for the determination of the most toxic PCB congeners.