Determination of polybrominated diphenyl ethers in fish tissue using gas chromatography-isotope dilution tandem...

Gas chromatography inductively coupled plasma triple quadrupole mass spectrometry (GC-ICP-MS/MS) operated in N₂O reaction mode (mass-shift mode) was established for the analysis of six congeners of polybrominated diphenyl ethers (PBDEs): BDE 28, BDE 47, BDE 99, BDE 100, BDE 153 and BDE 154 in fish samples. The spectral interference on the determination of PBDEs was eliminated by measuring the product ion (BrO⁺) instead of traditional methods measuring Br⁺. After comparing the signal intensities of the three reaction gases (O₂, H₂, and N₂O), the highest sensitivity was found using N₂O as the reaction gas. The results showed that bromine is an element that suffers from strong spectral overlap in ICP, mainly from Ar-based polyatomic interferences. Spectral interference was assessed by measuring the bromine isotope ratio of ⁸¹Br⁺ and ⁷⁹Br⁺ of the six priority PBDEs in the He collision mode and N₂O reaction mode, respectively. In the conventional He collision mode, the relative isotope ratio of ⁷⁹Br/⁸¹Br (the measured isotope ratio to the natural isotope ratio) of the analytes ranged from 0.955 to 0.965, which proves that using He as the collision gas cannot completely eliminate the spectral interference. In the N₂O reaction mode, the relative isotope ratio of ⁷⁹Br/⁸¹Br ranged from 0.991 to 1.004, demonstrating that spectral interference can be fully eliminated. Samples were processed using the modified QuEChERs method with detection limits ranging from 0.03 to 0.09 ng g^-1 with a relative standard deviation of less than 3%. Six priority PBDEs in the NIST reference materials SRM 1947 (frozen fish tissue homogenate) were determined by mass-shift mode to verify this conclusion. No statistically significant difference was observed between the measured value and the certified value, with recoveries between 95% and 114%. The method was applied to the analysis of PBDEs in marine fish samples and five PBDEs were observed (BDE28,BDE-47, BDE-99, BDE-100 and BDE-153) at concentrations ranging from 0.04 to 0.54 ng g^-1.