Mixed brominated/chlorinated dibenzo-p-dioxins, dibenzofurans and biphenyls: Simultaneous congener-selective determination in food

Of the 4600 individual poly-halogenated (bromo-chloro) dibenzo-p-dioxins, dibenzo-furans (PXDD/Fs) and 9180 poly-halogenated biphenyls (PXBs), 19 compounds were selected for analysis in food, based on current toxicological knowledge, chemical configuration, type and degree of halogenation, and the limited knowledge on environmental occurrence levels. The selection was also tempered by the availability of reliable analytical standards. The analytical methodology designed to allow simultaneous determination of PXDD/Fs and PXBs, was based on internal standardisation with 13C12 labelled compounds and high resolution mass spectrometry and involved a new separation procedure using dual activated carbon column fractionation. In order to unambiguously measure these compounds a practical, higher mass resolution (13,500–15,000 res) was used, coupled with a judicious choice of analyte ions and relative ion ratios. Further specificity was incorporated by exploiting the differences in chromatographic retention from those of potential interferants. The methodology was validated and used to measure occurrence levels of these contaminants in different matrices such as milk, meat, fish, eggs, offal, shellfish and soil. The limits of detection achieved by this methodology ranged from 0.005 to 0.02 ng kg−1 fat for foods. The analyses revealed the presence of both PXDD/Fs and PXBs, with the latter occurring to a greater extent, followed by PXDFs. This work represents the first targeted approach to measuring a range of individual PXDD/Fs and PXBs simultaneously.