Reliable enzyme immunoassay detection for chlorothalonil: fundamental evaluation for residue analysis and validation with gas chromatography.

This work describes the analytical performance of the enzyme-linked immunosorbent assay (ELISA) for the fungicide chlorothalonil to effectively exploit as a simple and rapid detection system for pesticide residue on the scenes of the agricultural production and distribution. This ELISA represents the satisfactory analytical characteristics (I50 value, 0.34 ng/g; limit of detection, 0.052 ng/g) to detect chlorothalonil at the regulatory values or thereabout in a sample. Noticeable cross-reactivities were shown with two fungicides, fthalide (58.8%) and pentachloronitrobenzene (quintozene) (20.0%), and some non-agrochemicals such as tetrachloroterephthalonitrile (96.8%) and tetrachlorophthalonitrile (68.3%). The influence of three organic solvents (methanol, acetone, and acetonitrile) used as extractants for chlorothalonil residue was evaluated, with the result that methanol was the most suitable solvent for the ELISA, and the final concentration in the well could be up to 5% (v/v) without any negative influence on the ELISA. It has been possible to directly analyze chlorothalonil residue only by giving dilution of each sample extract with water prior to the ELISA analysis. The average recovery values from the spiked samples by the ELISA were between 101.7 and 113.6% with the average coefficients of variation between 2.6 and 5.9%. Although the results obtained from the ELISA correlated well with those from the reference GC/MS methods for all agricultural samples (r>0.98), the linear function inclined to the ELISA results because of loss during complex sample preparations for GC/MS analysis. Nevertheless, the results demonstrated that the proposed ELISA is a reliable, cost-effective, and rapid quantitative method for chlorothalonil residue.