Determination of 18 Weakly Acidic Pesticide Residues in Fruits and Vegetables by Liquid Chromatography- Tandem Mass Spectrometry with QuEChERS Sample Preparation

A rapid method for the simultaneous determination of 18 weakly acidic pesticide residues including famoxadone in fruits and vegetables was developed using liquid chromatography- tandem mass spectrometry( LC- MS /MS). The samples were extracted with acetonitrile containing 1% acetic acid,and salted out with anhydrous magnesium sulphate and anhydrous sodium acetate. The extracts were cleaned up by dispersive solid phase extraction using C18 as sorbents. The ionization efficiency of famoxadone during atmospheric pressure ionization was studied. The result showed that ammonium acetate provided can significantly improve the ionization efficiency of famoxadone under negative electrospray ionization mode. Chromatographic analysis was carried out on a CSH C18 column using 5mmol /L ammonium acetate- acetonitrile as mobile phase by gradient elution. Pesticides were analyzed by negative electrospray ionization tandem mass spectrometry under multiple reaction monitoring mode. Quantification was achieved using matrix-matched standard calibrations as the external standard. Recoveries of 18 residues in 8 matrixes( broccoli,shallot,carrot,green bean,shiitake mushroom,apple,kiwifruit and orange) at fortification levels of 10,20,100 μg /kg ranged from 71. 4%to 119. 7% with relative standard deviations of 1. 2%- 10. 0%. The limits of quantitation( S /N≥10) were in the range of 0. 1- 2. 0 μg /kg. The method was simple,sensitive and environmental,and was suitable for monitoring 18 acidic pesticides residues in fruits and vegetables.