Background The pesticide residues in tea leaves are widely concerned. At present it is rarely reported that gas chromatography tandem mass spectrometry is used to simultaneously determine dicofol, chlorfenapyr, and six kinds of pyrethroids.

Objective This study aims to establish a method for simultaneous determination of dicofol, chlorfenapyr, and six kinds of pyrethroids in tea leaves by gas chromatography tandem mass spectrometry (GC-MS/MS) combined with QuEChERs method for pretreatment.

Methods First, 20 g tea leaves were accurately weighted into a centrifuge tube, soaked in water, shaken and extracted with acetonitrile-acetic acid, dehydrated with magnesium sulfate, and salted with sodium chloride. Second, the upper organic extracts were purified and centrifuged in a disperse solid phase extraction tube containing magnesium sulfate, N-propyl ethylenediamine, octadecylsilane bonded silica gel, and graphited carbon black, concentrated by nitrogen blowing, and then added with internal standard heptachlor exo-epoxide isomer B and ethyl acetate. After DB-5MS column separation, the target chemicals were determined by gas chromatography-tandem mass spectrometry with multireaction monitoring mode, quantified with retention time and ion pairs, and quantified by internal standard method. Retail tea leaf samples were collected to simultaneously determine dicofol, chlorfenapyr, and six kinds of pyrethriods according to the above established method, then the linear ranges, limits of detection, quantitative limits, recoveries, and precisions were calculated.

Results The linear ranges of the selected eight kinds of pesticides were 10-500 μg·L^-1, the correlation coefficients were all greater than 0.998, the method limits of detection (S/N=3) were 0.51-12.93 μg·kg^-1, the quantitative limits (S/N=10) were 1.69-43.10 μg·kg^-1. At three spiked levels of 0.150, 0.375, and 1.500 μg·kg^-1, the recoveries were from 74.4% to 110.0%, and the relative standard deviations were from 2.38% to 14.40% (n=7), all less than 20%. Of the collected tea leaf samples, 54 samples were detected positive of mixed pesticide residues, and 1 sample positive of single pesticide residues; 1 samples were unqualified for cyhalothrin, and 3 samples for fenvalerate.

Conclusion The method is easy, fast, and suitable for rapid screening and quantification of the eight pesticides in large quantities of tea samples.