MODULATED RESONANT EXCITATION OF SELECTED POLYCHLOROBIPHENYL MOLECULAR-IONS IN AN ION-TRAP MASS-SPECTROMETER

Modulated resonant excitation leading to collisionally induced dissoci ation (CID) of isolated molecular ions of di-ortho-, mono-ortho- and n on-ortho-substituted tetrachlorobiphenyl (PCB) compounds was accomplis hed in a quadrupole ion trap, While the ion trap was irradiated with a supplementary a.c. signal of fixed frequency, the r.f. drive voltage amplitude was modulated so as to sweep the ion absorption window. Modu lated resonant excitation of PCB molecular ions was carried out over a wide range of experimental conditions and congeners in order to compa re the relative stabilities of such ions and their fragmentation behav iour. Significant differences in both molecular ion stability and frag mentation patterns were observed for mono-ortho- and non-ortho-substit uted tetrachlorobiphenyls compared with di-ortho-isomers. Based on the differences in fragmentation patterns observed in CID mass spectra, a n analytical protocol is proposed for the ready determination of the t oxic mono-ortho- and non-ortho-substituted PCB congeners in mixtures o f PCBs. The protocol is based on the fragmentation behaviour of molecu lar ions, and is illustrated with a mixture of 13 PCB congeners.