Determination of 18 polychlorinated biphenyls in tea by gas chromatography-mass spectrometry coupled with dispersive solid-phase extraction

Abstract

A method for the rapid determination of 18 polychlorinated biphenyls (PCBs) in tea by gas chromatography-mass spectrometry (GC-MS) coupled with dispersive solid-phase extraction (dSPE) was developed and evaluated. Carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) and primary secondary amine (PSA) were used as sorbents in pretreatment process. PCBs were ultrasonically extracted from tea samples with hexane-acetone (1:1, v/v), and purified with the mixed sorbents of MWCNTs-COOH and PSA after replacing hexane-acetone by toluene. The PCBs were determined by an electron impact ionization source and selected ion monitoring mode. The analytes were qualitatively confirmed from the retention time and relative abundance ratio of characteristic ions, and quantified by a matrix-matched standard solution. The chromatographic and MS parameters influencing separation and sensitivity were optimized, and major factors affecting the extraction and cleanup efficiency including type and volume of extraction solvent, extraction time, type and amount of cleanup sorbent, and clean-up time were investigated. The performance of the method was evaluated. Under optimum conditions, satisfactory linear relationship was observed with the content of PCBs ranging from 5 to 500 μg/kg, with correlation coefficients (r) no less than 0.9998. The 18 PCBs in three kinds of tea matrices including Biluochun tea, Tieguanyin tea and Pu'er tea were spiked at 5, 10 and 100 μg/kg to evaluate recoveries, which ranged from 90.7% to 115.2% with relative standard deviations (n=5) between 0.3% and 10.9%. The limits of detection and the limits of quantification were 0.3-1.7 μg/kg and 5 μg/kg for each PCB, respectively. The method is simple, rapid, accurate, sensitive and effective, and is suitable for the determination of the 18 PCBs in different kinds of tea.