Evaluation of Performance of a Commercial Monoclonal Antibody–Based Fenitrothion Immunoassay and Application to Residual Analysis in Fruit Samples

Abstract

The performance of a commercially available enzyme-linked immunosorbent assay (ELISA) kit containing highly sensitive monoclonal antibodies against fenitrothion was assessed. The experimentally estimated dynamic range (0.087 to 2 ng/g) agreed with that established by the kit manufacturer (0.075 to 1 ng/g). The linearity of the standard curve produced for the kit-assembled standard solutions (slope = −0.3829) agreed with that of the curve produced for the self-made standard solutions (slope =−0.3619). The sensitivity (I50 value) and the limit of detection for the kit were 0.23 and 0.033 ng/g, respectively. Selectivity of the ELISA indicates that the monoclonal antibody can readily distinguish the target pesticide from other structurally related analogs and some metabolites (oxon forms), with the exception of ethyl O-(p-nitrophenyl) phenyl phosphonothionate (EPN), parathion-methyl, and parathion. Methanol was the best organic solvent for the kit, with optimal sensitivity observed at a final concentration in the well of 10% (vol/vol) or less. Matrix interferences were minimized by direct dilution with water (60-fold) of the methanolic extracts from apple and peach samples. To extract fenitrothion from these two agricultural products as simply and rapidly as possible, three extraction methods were used. The extraction method that involved shaking by hand for 3 min was the best among the three methods. High recovery percentages (116.6% for apple and 110.8% for peach) were obtained. Validation of the ELISA method was carried out using the gas chromatography–mass spectrometry method, resulting in high recovery and close correlation of results (r > 0.95). These findings strongly suggest that the ELISA kit may be routinely employed for on-site fenitrothion screening of fruit samples.