Monitoring of Diquat and Paraquat in Livestock Products by LC-MS/MS Combined with Modified QuEChERS Methods

The continued growth in domestic meat consumption has prompted the development of pesticide analytical methods for quality control of livestock products.Among the pesticides managed by national safety programs, diquat and paraquat pose a significant challenge for conventional multi-residual analysis due to their strong polarity and high solubility in water.The objective of this study was to develop analytical methods for diquat and paraquat to monitor their residues in livestock products distributed in domestic markets.Five livestock products such as beef, pork, chicken, milk and eggs were selected as typical test samples.The analytical methods of diquat and paraquat were established by optimizing all the steps to meet with the criteria of CODEX guidelines.The optimized extraction methods were achieved by using the mixtures of water and acetonitrile containing 0.5% formic acid as the extraction solvent and acetonitrile containing 0.5% formic acid as the subsequent extraction solvent.C 18 dispersive solid-phase extraction was found to be effective for sample clean-up prior to LC-MS/MS analysis.The standard calibration curves of diquat and paraquat showed good linearity with the coefficients of determination (R 2 ) ranging from 0.9902 to 0.9986 for diquat and from 0.9968 to 0.9997 for paraquat.The established methods achieved recoveries ranging from 66.5 to 100.4% for diquat and ranging from 73.5 to 95.6% for paraquat.A total of 409 livestock samples from domestic markets were investigated for monitoring of diquat and paraquat by the established methods coupled with LC-MS/ MS.Diquat and paraquat were found in the livestock samples at levels below the limit of quantitation (0.01 mg/kg).The analytical methods developed in this study could be successfully applied for monitoring diquat and paraquat in real livestock samples from domestic markets.