Determination of ultra-trace levels of priority PBDEs in water samples by isotope dilution GC(ECNI)MS using 81Br-labelled standards

A gas chromatography electron capture negative ionization mass spectrometry (GC(ECNI)MS) procedure for the determination of priority polybrominated diphenyl ethers (PBDEs; congeners 28, 47, 99, 100, 153 and 154) in water samples at regulatory EU levels has been developed. The method is based on the use of ⁸¹Br-labelled PBDEs for isotope dilution analysis and the measurement of ⁷⁹Br/⁸¹Br isotope ratios in gas chromatography peaks with the electron capture negative ionization technique. The suitability of this ion source for the precise and accurate measurement of bromine isotope ratios has been demonstrated. The general ECNI-IDMS procedure was evaluated by the analysis of NIST SRM 1947 (Lake Michigan fish tissue) with satisfactory results. For the analysis of water samples, 500 mL of the samples were spiked with the labelled PBDEs and extracted with 10 mL isooctane for 30 min. The extract was evaporated down to ca. 100 μL and injected in the GC(ECNI)MS. Detection limits ranged from 0.014 ⁻¹ to 0.089 pg mL⁻¹ depending on the congener. Recoveries from real water samples, spiked at a level of 0.5 pg mL⁻¹, ranged from 77% to 102%.