A method using QuEChERS sample preparation with liquid chromatography polarity-switching tandem mass spectrometry was developed and validated for the analysis of quinclorac and its degradation product quinclorac methyl ester in canola seed. The method was used to analyse canola treated with quinclorac, harvest sample composites and samples of canola shipments. Quinclorac residues were present in all samples of canola treated with a quinclorac-containing herbicide that were analysed. Quinclorac was found in 93% of samples, with an average of 0.018 mg kg(-1). All samples contained quinclorac methyl ester, with an average of 0.061 mg kg(-1). The average concentration of total residues (as quinclorac equivalents) on treated canola was 0.075 mg kg(-1), with a range of 0.016-0.124 mg kg(-1). The observed residues were all at least 10 times lower than the Canadian maximum residue limit of 1.5 mg kg(-1). Quinclorac and quinclorac methyl ester were not found in any harvest and export composite samples, which represented the majority of canola grown in western Canada in 2015 and canola exported in late 2015. Even though usage of quinclorac-containing herbicide on canola can result in the presence of low concentrations of residues, the absence of quinclorac residues in harvest and shipment samples suggests that use of quinclorac-containing herbicide was not widespread, and that any residues present were diluted as canola was combined along the grain-handling chain into shipment lots, or segregated and prevented from entering shipment lots.
Keywords: LC-MS/MS; Pesticide; grain; method validation.