Liquid chromatographic method for determination of diquat and paraquat herbicides in potatoes: collaborative study.
A liquid chromatographic (LC) method for the determination of diquat and paraquat herbicides/desiccants in potatoes was collaboratively studied in 6 laboratories. Analytes are extracted from 5 g sample with dilute acid by using a microreflux procedure; the hydrolysate is adjusted to pH 9-10 and passed through a disposable silica cartridge for rapid cleanup and preconcentration. Analytes are separated on a reversed-phase LC column and are measured as their heptanesulfonate ion pairs by UV detection. Each collaborator determined diquat and paraquat at 4 levels (0.05, 0.1, 0.5, and 1.0 ppm) in blind duplicate samples plus 2 blind negative control samples. Potatoes, obtained from each participant's region, were spiked by the collaborators with unknown aqueous solutions containing no analyte or a mixture of diquat and paraquat standards. Repeatability and reproducibility relative standard deviations (RSDr and RSDR) averaged 17.1 and 29.0%, respectively, for determination of diquat and 10.8 and 29.5%, respectively, for paraquat. For analysis of standard solutions, RSDr and RSDR values were 6.3 and 12.0%, respectively, for diquat and 7.3 and 13.9%, respectively, for paraquat. Accuracy, measured by comparison with true spiking values (absolute recovery) averaged 77.6 and 76.2% for diquat and paraquat, respectively, and ranged from 71.8 to 88.0% for both compounds. The method was adopted first action by AOAC International.
Health and Welfare Canada, Bureau of Chemical Safety, Ottawa, ON.
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Worobey
D002853:Chromatography, Liquid; D004178:Diquat / Q000032:analysis*; D006540:Herbicides / Q000032:analysis*; D007202:Indicators and Reagents; D010269:Paraquat / Q000032:analysis*; D010573:Pesticide Residues / Q000032:analysis*; D015203:Reproducibility of Results; D011198:Solanum tuberosum / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet
D006540:Herbicides; D007202:Indicators and Reagents; D010573:Pesticide Residues; D004178:Diquat; D010269:Paraquat