Determination of pesticides in tea by isotope dilution gas chromatography-mass spectrometry coupled with solid-phase microextraction

摘要

The aim of this study was to develop a headspace solid-phase microextraction/gas chromatography-isotope dilution mass spectrometry (HS-SPME/GC-IDMS) method for the simultaneous quantification of 8 pesticides in tea samples. The thermodynamic equilibrium between analytes and isotope labeled analogues was studied in this paper. In addition, different parameters affecting pesticide extraction by HS-SPME were considered and optimized, including type of fiber coating, extraction temperature/time, and desorption temperature/time. In the optimized method, the isotopic labels spiked in incurred samples were equilibrated for 15 min before HS-SPME, and analytes were absorbed for 70 min at 70 ?°C in the sample headspace with a 100 ??m polydimethylsiloxane (PDMS) fiber. By using the isotopic dilution technique, the relative standard deviation (RSD) for 8 analytes was improved to 3.7a€“10.2%, compared with the values of 6.5a€“26.7% using the traditional external standard method. The recoveries were between 86.7 and 112.8%, and the limits of detection (LODs) ranged from 1.2 to 19.6 ng ga?’1 (except cypermethrin, 22.1 ng ga?’1). Compared with the conventional sample preparation methods, the proposed method has the advantage of being quick, easy to operate, highly sensitive and also solvent saving. The optimized HS-SPME/GC-IDMS method was not only suitable for qualitative analysis but also could be successfully applied to the quantitative analysis of pesticides in tea.