Analysis of Indoxacarb Enantiomers and its Seven Metabolites in Tea and Tea Infusion by Ultra Performance Liquid Chromatography Tandem Triple Quadrupole Mass Spectrometry

A residual analysis method of indoxacarb enantiomers and its seven kinds of degradation products in fresh leaves, green tea, black tea, green tea infusion and black tea infusion was established, followed by comparing the extraction solvent with different pH, purification and enrichment capacity of different solid phase extraction column, different loading volume and different proportion of eluting solvent. Fresh tea leaves, black tea and green tea samples were extracted by acetonitrile and water, purified by C18 and GCB dispersive solid phase extraction. After concentrated nearly to dry, methanol-water (9∶1, V/V) was used to resolve the sample. PRP SPE column was used for the enrichment and purification of green tea infusion and black tea infusion, then methanol-water (4∶6, V/V) was used to cleanup pigments and other impurities. Finally, the analytes were eluted by methanol, and after rotary to dryness, reconstituted with methanol-water (9∶1, V/V). The indoxacarb enantiomers and its degradation products were separated by Lux^® 3 μm Cellulose-2 column and quantified by UPLC-MS/MS using matrix external standard method. In the concentration ranged of 0.005-5 mg/L, the correlation coefficients of different matrix standard curves were above 0.999 1. The average recoveries of indoxacarb enantiomers and degradation products at three spiked concentration levels ranged from 76.9% to 108.4% with the relative standard deviation (RSD) less than 16.4%. The limits of detection (LODs) in fresh leaves, black tea and green tea were 0.001 mg/kg, and that in black tea infusion and green tea infusion were 0.2 μg/L. The limits of quantification (LOQs) in fresh leaves, black tea and green tea were not higher than 0.01 mg/kg, and that in black tea infusion and green tea infusion were not more than 1 μg/L. The results show that the standard curves, correlation coefficients, recoveries and precisions of this method can meet the requirements of pesticide residue analysis, and it can be used for the determination and screening of indoxacarb enantiomers and degradation products in tea and other samples.