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

Abstract

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 μm polydimethylsiloxane (PDMS) fiber. By using the isotopic dilution technique, the relative standard deviation (RSD) for 8 analytes was improved to 3.7–10.2%, compared with the values of 6.5–26.7% 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 g⁻¹ (except cypermethrin, 22.1 ng g⁻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.