EVALUATION OF ELISA MICROTITER PLATE-BASED ASSAYS FOR THE DIRECT DETERMINATION OF ISOPROTURON IN WATER SAMPLES AND SOIL EXTRACTS

Trials were carried out on the commercially available Millipore isopro turon ELISA microtiter plate tests and on laboratory assays developed by Hirst as part of a Joint European Union research project (BIOPTICAS ). The lowest detectable dose (LDD) was determined as three times the standard deviation of the blanks. Depending on the calibration curves obtained on different days with different plates, the LDD varied from 0.020 to 0.064 mu g/L for the Millipore test and from 0.080 to 0.329 m u g/L for the Hirst test. The mean coefficients of variation within a single plate for triplicate determinations of standard solutions in th e 0.05 to 0.5 mu g/L range were 5.5 and 3.6% for Millipore and Hirst r espectively. Cross-reactivity was studied for mono- and di-demethylate d isoproturon, chlortoluron, diuron and linuron. The highest cross-rea ctivity with both tests was that of mono-demethylated isoproturon (22% for Millipore, 4% for Hirst). This molecule was the only one to show significant cross-reactivity in the Hirst test, whereas in the Millipo re test, the di-demethylated isoproturon also crossreacted (4%). Natur al water samples, 19 ground-, 53 lysimetric plate and 47 suction cup w ater samples, and 32 soil samples were also analysed with the ELISA te sts. HPLC with a diode array detector was used as a validated control technique for the natural samples. For each water type, ELISA concentr ations of both tests were significantly correlated with the HPLC value s (r greater than or equal to 0.937; p < 0.001). For the soil extracts , the correlations were also significant (p < 0.001), but the scatter in the data was greater. Overall, the Millipore correlation coefficien ts were higher than those of Hirst. (C) 1997 Elsevier Science Ltd.