Comparison of an enzyme-linked immunosorbent assay and a gas chromatographic procedure for the determination of molinate residues.

An enzyme-linked immunosorbent assay (ELISA) was compared to a gas chromatographic method for the analysis of the thiocarbamate herbicide molinate (S-ethyl hexahydroazepine-1-carbothioate). Apparent recoveries from water spiked at 1 ppb to 1 ppm levels were comparable when liquid-liquid extraction was used. Solid-phase extraction was also examined and apparent recoveries by both ELISA and gas chromatography (GC) were comparable to each other as well as to the liquid-liquid extraction method. Methanol, acetonitrile, and ethyl acetate were equally effective in eluting molinate from solid-phase columns. An excellent correlation was obtained between the ELISA and GC method for field-treated water samples extracted by using the solid phase method and either ethyl acetate or methanol as the eluting solvent. Air and soil samples from this same study correlated well when analyzed by ELISA or GC, but ELISA results for soil were generally higher than GC data and of slightly lower precision than GC. Tests with a coated plate, pipettors, and the plate reader amounted to 8.0% error, the majority of which was attributable to the coating antigen binding and to antigen-antibody reactions.