A comparison of three mass spectrometric methods for the determination of dioxins/furans

A comparison is presented of the performances of three mass spectrometers of high specificity in the determination of dioxin/furan congeners. The three instruments used in this study were a triple-sector EBE mass spectrometer operated at high mass resolution (HRMS), a quadrupole ion trap (QIT) mass spectrometer, and a triple-stage quadrupole (TSQ) mass spectrometer. The QIT and TSQ instruments were operated in tandem mass spectrometric mode. A mixture of tetra- to octa-chlorodibenzo-p-dioxins (T-4-O8CDD) containing in all seven dioxin congeners was used for much of this study. The factors considered in this comparison were the tuning of each instrument, the preparation and comparison of calibration curves, the 2,3,7,8-T4CDD detection limit for each instrument, ion signals due to H(6)CDDs obtained with each instrument from two real samples (air and pyrolysed polychlorinated phenols), average relative response factors, and ionization cross sections. For each dioxin congener, the response factor is expressed relative to that for the O8CDD congener, whereas the electron impact ionization cross section is expressed relative to that for the T4CDD congener. The relative ionization cross sections for T-4-O8CDD from HRMS and QIT, and for T-4-P5CDD from TSQ are in good agreement, and show an overall decrease of some 10-20% with increasing degree of chlorine substitution; the variation among three H6CDD congeners is identical in each case. With TSQ, lower relative ionization cross sections for H-6-O8CDD are ascribed to mass-dependent fragment ion scattering in the RF-only collision cell. (Int J Mass Spectrom 194 (2000) 235-246) (C) 2000 Elsevier Science B.V.