Isomer-selective determination of tetrachlorodibenzo-p-dioxins using hydroxyl negative ion chemical ionization mass spectrometry combined with high-resolution gas chromatography.

Abstract

OH/sup -/ negative ion chemical ionization (NICI) mass spectrometry can be used for the isomer-specific determination of tetrachlorodibenzo-p-dioxins (TCDDs). When CH/sub 4//N/sub 2/O mixtures are used as a reagent gas, (M - H)/sup -/, M/sup -/, (M + OH)/sup -/, and (M - Cl)/sup -/ are formed in the ion source. When this technique is combined with high-resolution gas chromatography, 14 isomers including 2,3,7,8-TCDD can be identified by significant differences in the abundances of these ions. Monitoring of the (M + OH)/sup -/ adduct ion (formed by attack of the dioxin ring) allows an increase in the selectivity for TCDDs against polychlorinated biphenyls, pesticides, etc. A detection limit of 25 pg at m/z 337 (M + OH)/sup -/ (signal-to-noise 10:1) was obtained under standard conditions.