Determination of Residues of 36 Pesticides in Fruit and Vegetable Juice by Ultra High Performance Liquid Chromatography-Tandem Mass Spectrometry with Magnetic Graphene Solid Phase Extraction

2.00 g of the fruit and vegetable juice sample was taken and placed in a 50 mL-centrifuge tube. 20 mL of acetonitrile was added, and the mixture was vortexed for 2 min and centrifuged for 5 min. The extraction of the residue was repeated with 20 mL of acetonitrile, and the supernatants were combined. The mixture was rotary evaporated to dryness, and 10 mL of 10% (volume fraction, the same below) acetonitrile solution was added to dissolve. 40.0 mg of magnetic graphene (prepared by chemical co-precipitation method) was added, and the mixture was vortexed for 20 min. The sediment was collected by a magnet, and the supernatant was discarded. 1.0 mL of acetone was added and the solution was vortexed for 1 min. The elution was repeated twice. All supernatants were combined and blown to drynesss by nitrogen, and made its volume up to 1 mL with 10% acetonitrile solution. The residues of 36 pesticides were determined by ultra high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). Agilent Eclipse Plus C₁₈ column was used as the stationary phase and the mixed solution composed of 0.1% (volume fraction) formic acid solution and acetonitrile at different volume ratios was used as the mobile phase for gradient elution．Electrospray ion (ESI) source was used for mass spectrometry. The targets were analyzed by multiple reaction monitoring (MRM) mode in positive ion (ESI⁺) scanning mode. As shown by the results, linear relationships between the corresponding quantitative ion response peak areas and mass concentrations of 36 pesticides were kept in definite ranges, with detection limits (3S/N) in the range of 0.001-0.006 mg·kg^-1. Test for recovery was made by the standard addition method, giving results in the range of 61.3%-104%, with RSDs (n=6) of the determined values less than 12%. This method could be used to determine the residues of 36 pesticides in 20 actual fruit and vegetable juices, and carbofuran, imidacloprid, carbendazim, oxytetracycline, and clotrimazole were detected in some samples, with the detection amounts in the range of 0.010-0.034 mg·kg^-1.