Determination of Residues of 22 Carbamate Pesticides in Green Citrus Tea by High Performance Liquid Chromatography-Tandem Mass Spectrometry with QuEChERS

The even powder sample of green citrus tea (2.00 g) was taken and placed into a 50 mL-plastic centrifuge tube, and soaked by about 5 mL of the distilled water for 10 min. The analytes were extracted with 20.0 mL of acetonitrile and QuEChERS salt package (4 g of MgSO₄ and 1 g of NaCl) for 1 min and then centrifuged for 5 min. An aliquot (8 mL) of the extract was taken and purified by QuEChERS purification tube containing 1 200 mg of MgSO₄, 400 mg of C18, 400 mg of N-propylethylenediamine (PSA) and 200 mg of graphitized carbon black (GCB), and 2 mL of the supernatant was passed through 0.22 μm needle type organic phase filter membrane. The 22 carbamate pesticides in the filtrate were determined by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) using Zorbax-Eclipse-Plus C₁₈ column as the stationary phase, and a mixture of methanol and 5 mmol · L⁻¹ ammonium acetate solution containing 0.1%(volume fraction) formic acid at different volume ratios as the mobile phase for gradient elution. The electrospray ion (ESI) source was used for mass spectrometry analysis in the multiple reaction monitoring (MRM) mode, and the matrix matching method was used for quantification. As shown by the results, linear relationships between the values of the corresponding peak area and mass concentration of 22 pesticides were found in the range of 0.5-20.0 μg · L⁻¹, with lower limits of determination (10S/N) in the range of 0.001-0.01 mg · kg⁻¹. Test for recovery was made by the standard addition method, giving results in the range of 76.7%-107%, with RSDs (n=6) of the determined values in the range of 0.70%-9.7%. This method was used for analysis of 30 batches of green citrus tea samples, and a total of 5 pesticides, including carbofuran, trihydroxycarbofuran, fenobucarb, propoxur and methiocarb, was detected, with detection rate more than 90.0%. Among them, the detection amounts of carbofuran, trihydroxycarbofuran, and fenobucarb were 0.01-0.76 mg · kg⁻¹, 0.02-0.08 mg · kg⁻¹, and 0.01-0.03 mg · kg⁻¹, respectively. The detection amounts of most pesticides exceeded the limit value (0.02 mg · kg⁻¹) specified in GB 2763—2021.