Comparison of immunoassay with a conventional method for the determinationof Diazinon (R) in surface waters

The National Laboratory for Environmental Testing (NLET) has successfully u sed immunoassay as a screening technique to detect the presence of organic contaminants. A Beacon Analytical Systems Inc., InSite (TM) Diazinon Plate Kit was tested for its ability to identify Diazinon((R)) {O,O-diethyl-O-(2[ -methylethyl]4-methyl-6-pyrimidinyl)phosphorothioate} in a surface water kn own to have agricultural inputs from organophosphate pesticide (OP) applica tions. 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, thr ee had GC concentrations below the detection limit of the test kit, which w ould imply these immunoassay values included responses due to cross-reactiv ity with other compounds. Based on the limited data set, application of imm unoassay for screening the presence of diazinon at our test site did not ap pear favorable. Differences in sample storage conditions were not expected to contribute to differences, but may have to be re-examined. (C) 2001 Else vier Science B.V. All rights reserved.