Simultaneous Determination of Thiophanate-Methyl and Its Metabolite Carbendazim in Tea Using Isotope Dilution Ultra Performance Liquid Chromatography–Tandem Mass Spectrometry

A rapid method has been developed for the determination of thiophanate methyl and its metabolite carbendazim in tea samples using ultra-high-performance liquid chromatography tandem mass. Dispersive solid-phase extraction was optimized and employed as a sample preparation technique without concentration and solvent exchange. Degradation of thiophanate methyl and its isotope were observed and they declined at the similar rate during sample preparation. The results showed that calibration by isotope internal standards was reliable to correct the degradation. With the extraction solvent at pH range of 2.3-10.3, difference for thiophanate methyl degradation was not much significant due to the buffer action of tea matrix solution. Matrix effects were dependent on the nature of the analytes and tea categories, but calibrated effectively by isotope internal standards. Recoveries ranged 97.2-110.6%, and relative standard deviations were <25.0%. The limit of quantification was both 0.010 mg kg(-1) for thiophanate methyl and carbendazim. The developed method was utilized to measure concentrations of thiophanate methyl and carbendazim in tea samples from seven provinces of China, as well as to investigate the degradation of thiophanate methyl in tea crop.