Determination of 22 Pesticide Residues in Cowpeas and Mangoes by One-step QuEChERS Combined with Ultra Performance Liquid Chromatography-Mass Spectrometry

A one-step QuEChERS automated detection technology for 22 pesticides in cowpeas and mangoes was established based on ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The sample was extracted by acetonitrile containing 1% acetic acid, added with EN extraction salt (anhydrous Mg2SO4, sodium chloride, trisodium citrate dihydrate, disodium hydrogen citrate sesquihydrate) to remove water, and then purified with C18 and graphitized carbon black (GCB). The target analytes were separated by ACQUITY UPLC BEH C18 chromatography column, using 0.01% formic acid aqueous solution (containing 2 mmol/L ammonium formate)-0.01% formic acid methanol as the mobile phase, and determined in multiple reaction monitoring (MRM). The results showed that the 22 pesticides had good linearity in the range of 0.01~25.00 µg/L, with coefficient of determination (R2) higher than 0.994. The limits of detection (LOD, S/N=3) were 0.05~2 µg/kg, and the limits of quantification (LOQ, S/N=10) were 0.1~5 µg/kg. At the spiked levels of 1×LOQ, 2×LOQ, and 10×LOQ, the average recoveries for cowpeas were 70.9%~116.6%, 71.9%~118.3%, and 73.7%~113.7%, respectively, and for mangoes were 70.2%~114.6%, 71.2%~113.7%, and 74.3%~118.5%, respectively. The relative standard deviations for them were all within 20%. The method was successfully applied to the detection of 42 actual samples, and 33 samples detected pesticide residues. This method has high sensitivity and a satisfactory level of automation, effectively reducing human operation steps. It is suitable for the simultaneous detection and accurate quantification of 22 pesticides and their metabolites.