Determination of 37 Pesticide Residues in Tea by Gas Chromatography£­Tandem Mass Spectrometry Combined with QuEChERS and Prepositive Internal Standard

KeyWord:gas chromatography£­tandem mass spectrometry£¨GC£­MS/MS£©  QuEChERS  prepositive internal standard  tea  pesticide residues

Abstract:

      A gas chromatography£­tandem mass spectrometry£¨GC£­MS/MS£© combined with QuEChERS plus prepositive internal standard was developed for the simultaneous detection of 37 pesticide residues in tea. The target pesticides included 14 organophosphorus pesticides£¬10 organochlorine pesticides£¬8 pyrethroid pesticides and 5 organic heterocyclic pesticides. The effects of different extraction solvents£¬water amounts and internal standard adding approaches on extraction were studied. The matrix effects of 37 pesticides in different types of tea were also explored. The optimal experimental conditions were as follows£ºfirstly£¬the tea samples were soaked for 30 min with 10 mL water after adding heptachlor epoxide as internal standard£¬then the target pesticides were extracted ultrasonically using 20 mL acetonitrile for 20 min£¬followed by adding QuEChERS extract pouch£¨containing 6 g magnesium sulfate and 1.5 g sodium acetate£©. After vortexing evenly and centrifugation£¬10 mL of the supernatant was separated and transferred into QuEChERS purge tube which contained a mixed sorbent of 1 200 mg magnesium sulfate£¬400 mg primary secondary amine£¨PSA£©£¬400 mg C18 and 400 mg graphitized carbon black£¨GCB£©. The mixtures were vortexed evenly and centrifugated. Then 2 mL of the purified solution was concentrated by nitrogen blowing at 40 ¡æ until the solution was nearly desiccated. After that£¬1 mL ethyl acetate was used to redissolve the residues. Finally£¬the target pesticides were detected by GC£­MS/MS in multiple reaction monitoring£¨MRM£© mode£¬and quantified by the internal standard method with matrix matching standard curve. The results showed that the use of prepositive internal standard had a better recovery result than the use of postpositive internal standard. Chromatogram signals of most pesticides in green tea£¬black tea£¬white tea and dark tea matrices were enhanced distinctly. Under the optimized conditions£¬good linear relationships were observed for the 37 pesticides£¬and the correlation coefficients£¨r2£© were greater than 0.99. The limits of detection£¨LODs£© and the limits of quantitation£¨LOQs£© were in the range of 0.2£­15.7 ¦Ìg/kg and 0.7£­52.2 ¦Ìg/kg£¬respectively. The recoveries for 37 pesticides at three spiked levels£¨the LOQ£¬2 times the LOQ and 10 times the LOQ£© ranged from 70.2% to 120%£¬with relative standard deviations£¨RSDs£© of 1.1%£­11%. This method has the features of simple operation£¬high accuracy£¬high efficiency and low cost£¬which could be applied to the routine detection of pesticide residues in tea.