Dispersive liquid-liquid microextraction and gas chromatography-mass spectrometry determination of polychlorinated biphenyls and polybrominated diphenyl ethers in milk

An effective multi‐residue pretreatment technique, solid‐phase extraction (SPE) combined with dispersive liquid–liquid microextraction (DLLME), was proposed for the trace analysis of 14 polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in milk samples using gas chromatography–mass spectrometry (GC‐MS). Interesting analytes in milk samples were extracted with hexane after protein precipitation. The hexane extracts were loaded on an LC‐Florisil column to isolate analytes from the milk matrix. The elutes were dried and dissolved in acetone, which was used as the disperser solvent in subsequent DLLME procedures. The effects of several important parameters on the extraction efficiency were evaluated. Under the optimized conditions, a linear relationship was obtained in the range of 0.02–10.00 μg/L (PCBs) and 0.5–100.00 μg/L (PBDEs). The LOD (S/N=3) and relative standard deviations (RSDs, n=5) for all analytes were 0.01–0.4 μg/L and 0.6–8.5%, respectively. The recoveries of the standards added to raw bovine milk samples were 74.0–131.8%, and the repeatabilities of the analysis results were 1.12–17.41%. This method has been successfully applied to estimating PCBs and PBDEs in milk samples.