Tandem mass spectrometric determination of polychlorodibenzo-p-dioxins and polychlorodibenzofurans in a quadrupole ion trap using multi-frequency resonant excitation

A tandem mass spectrometric analytical method is presented for the concurrent determination of tetra-to octa-chlorodibenzo-p-dioxins and tetra-to octa-chlorodibenzofurans. The method entails operation of a quadrupole ion trap mass spectrometer wherein two isolated molecular ion species are fragmented by irradiation with a band of multiple frequencies for a period of but 10 ms. Up to three co-eluting compounds have been determined individually using a software program, Toolkit, which permits successive activation of multiple scan functions customized for each compound and optimized for the resonant excitation conditions employed. Two calibration curves have been obtained for each compound over a 400-foId concentration range; one calibration curve is based on the single major fragmentation channel of COCl.-loss while the other is based on multiple fragmentation channels. The CID efficiency, defined as the signal ratio of fragment ions detected from the major dissociation channels to molecular ions isolated, was 0.80-0.90 for all chlorocongeners. The calibration curves were prepared using a set of standard solutions containing labelled chlorocongeners. Optimum results were obtained when fragment ion signal intensities were normalized to those obtained from a single standard solution. In general, tandem mass spectrometric response factors display a 4-fold range with response factor decreasing with increasing chlorine substitution. (C) 1997 Elsevier Science B.V.