Validation of a pressurized solvent extraction and GC–NCI–MS method for the low level determination of 40 polybrominated diphenyl ethers in mothers’ milk

This study reports an efficient method for the determination of 40 PBDEs from mono- to hepta-brominated in human milk. Pressurized liquid extraction (PLE) was optimized to recover PBDEs in a quantitative way using 1 g of freeze dried milk. Due to the great amount of coextracted compounds, the clean-up step was optimized using alumina SPE disposable cartridges of 2 and 5 g. Whereas 2 g alumina SPE failed in providing good extraction yields, all PBDEs were satisfactorily recovered using 5 g alumina SPE cartridges. Detection was performed with gas chromatography coupled to mass spectrometry with negative chemical ionization and method detection limits ranged from 0.01 to 0.05 μg kg−1 wet weight (ww) with a good intra and inter-day variation (coefficient of variation lower than 13.4%). This method was validated by participating in an interlaboratory exercise from Quasimeme (United Kingdom), where a standard solution containing seven congeners and a certified unspiked mothers’ milk were analyzed. In the standard mixture, levels between 96.915 and 570.172 μg l−1 were quantified, whereas in certified mothers’ milk, BDEs 47, 99, 100 and 154 were detected at levels from 0.010 and 0.061 μg kg−1 ww, with an error <30%. The applicability of the method was tested experimentally in five mothers’ milk samples, where only BDE 47 was detected at a maximum concentration of 10.45 μg kg−1 lipid weight (lw). PLE succeeded in extracting all PBDEs from the sample with good reproducibility although the clean-up step had to be severely performed to eliminate sample interferences such as milk lipids and proteins.