Comparison of immunoassay with a conventional method for the determination of Diazinon® in surface waters Original Research Article

The National Laboratory for Environmental Testing (NLET) has successfully used immunoassay as a screening technique to detect the presence of organic contaminants. A Beacon Analytical Systems Inc., InSite™ Diazinon Plate Kit was tested for its ability to identify Diazinon® {O,O-diethyl-O-(2[-methylethyl]4-methyl-6-pyrimidinyl)phosphorothioate} in a surface water known to have agricultural inputs from organophosphate pesticide (OP) applications. The quantitative accuracy of test kit results were compared against the conventional NLET gas chromatography (GC) method. Of 21 OP observations using the conventional method, 15 were at or below the detection limit of the immunoassay kit, 4 were observed and 2 were not detected. There were no false positives, but overall precision amongst immunoassay replicates was poor (CV>50%). All immunoassay results were biased high compared to their corresponding GC concentrations. Of the four immunoassay observations, three had GC concentrations below the detection limit of the test kit, which would imply these immunoassay values included responses due to cross-reactivity with other compounds. Based on the limited data set, application of immunoassay for screening the presence of diazinon at our test site did not appear favorable. Differences in sample storage conditions were not expected to contribute to differences, but may have to be re-examined.