Development of immunoassays for the analysis of chlorpyrifos and its major metabolite 3,5,6-trichloro-2-pyridinol in the aquatic environment

Competitive enzyme-linked immunosorbent assays (ELISA) for chlorpyrifos and its major degradation product, 3,5,6-trichloro-2-pyridinol (TCP), were developed, and their suitability for the determination of these analytes in environmental waters was studied. Immunoassays were based on specific, high affinity monoclonal antibodies obtained from simple haptens. For standards, limits of detection of the ELISA were 6 ng ml−1 chlorpyrifos and 0.034 ng ml−1 TCP. No significant cross-reactivity for related compounds was observed, and chlorpyrifos could be measured without the interference of TCP and vice versa. As a general rule, water samples had to be diluted at least 1/5 for the chlorpyrifos analysis to minimize matrix effects, while TCP could be directly analyzed in the waters tested with no significant interference. Under these conditions, the analyte recoveries from spiked water samples ranged from 87 to 116% for chlorpyrifos, and from 78 to 112% for TCP. The TCP immunoassay could be used to determine levels as low as 0.1 ng ml−1 TCP in environmental waters without previous extraction or cleanup.