Development of an LC-MS/MS method for simultaneous analysis of commercial biological pesticides residues in vegetables
Abstract
A reversed-phase LC-MS/MS method was developed for simultaneous determination of residues of the 3 following pepticides in vegetables: abamectin, emamectin, and azadirachtin. The method was optimized and finally established as: Column - Agilent Poroshell 120 Phenyl - Hexyl (150 mm x 4.6 mm x 2.7 µm); Mobile phase – MeOH-formic acid 0.1 % (in gradient mode); Flow rate - 0.7 to 0.9 ml/min; Injection volume - 10 μl; Detection - Electrospray ionization source operated in positive and multi reaction monitoring (MRM) mode with the transition of m/z 895.5 " 183, m/z 885.5 " 158 and m/z 743.3 "725 for ABA, EMA, and AZA, respectively. Validation by EC-657/2002 guideline showed the method meeting all the requirements of wide linearity range of 0.5 – 150 ppb, high correlation coefficients (R2 > 0.9984), very good accuracy (recovery rate 93.3 – 104.5 %) and moderate precision (RSD < 10 %), typical LOD, LOQ (0.00002 - 0.2 ppb and 0.00005 - 0.5 ppb for three bio-pesticides). For practical test, 24 real samples were analyzed and surveyed; the target pesticide residues were found below MRLs in three vegetable samples (12.5 %). Particularly, emamectin was found at high levels (16.2 ppb) in V.02-S3 samples, much higher than MRLs by the Vietnam Ministry of Health.
