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.