TANDEM MASS-SPECTROMETRIC DETERMINATION OF POLYCHLORODIBENZO-P-DIOXINS AND POLYCHLORODIBENZOFURANS IN A QUADRUPOLE ION-TRAP USING MULTIFREQUENCY RESONANT EXCITATION

A tandem mass spectrometric analytical method is presented for the con current determination of tetra-to octa-chlorodibenzo-p-dioxins and tet ra-to octa-chlorodibenzofurans. The method entails operation of a quad rupole ion trap mass spectrometer wherein two isolated molecular ion s pecies are fragmented by irradiation with a band of multiple frequenci es for a period of but 10 ms. Up to three co-eluting compounds have be en determined individually using a software program, Toolkit, which pe rmits successive activation of multiple scan functions customized for each compound and optimized for the resonant excitation conditions emp loyed. Two calibration curves have been obtained for each compound ove r a 400-foId concentration range; one calibration curve is based on th e 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 dissociat ion channels to molecular ions isolated, was 0.80-0.90 for all chloroc ongeners. The calibration curves were prepared using a set of standard solutions containing labelled chlorocongeners. Optimum results were o btained when fragment ion signal intensities were normalized to those obtained from a single standard solution. In general, tandem mass spec trometric response factors display a 4-fold range with response factor decreasing with increasing chlorine substitution. (C) 1997 Elsevier S cience B.V.