Practical immunochemical method for determination of 3,5,6-trichloro-2-pyridinol in human urine: Applications and considerations for exposure assessment

An analytical method is described for the quantitative determination of 3,5,6-trichloro-2-pyridinol (3,5,6-TCP) in human urine. This is the primary analyte found in urine as a result of exposure to chlorpyrifos, chlorpyrifos-methyl, triclopyr, or 3,5,6-TCP. Conjugates of 3,5,6-TCP are released from urine by acid hydrolysis. The free 3,5,6-TCP is purified using C-18 solid-phase extraction, eluting the analyte with 1-chlorobutane. An aliquot of 1-chlorobutane is placed in a vial containing Trichloropyridinol Sample Diluent and evaporated, leaving the 3,5,6-TCP in the aqueous sample diluent. The samples are assayed using the Trichloropyridinol RaPID Assay immunoassay test kit. Final results are calculated using a standard curve constructed by linear regression after a In/Logit data transformation is performed of the concentration and the absorbance readings, respectively. The calculated lower limit of quantitation for 3,5,6-TCP in fortified control urine samples is 2.96 ng/mL (2.96 ppb). Residues of 3,5,6-TCP determined using both immunochemical and gas chromatography with mass spectrometric detection correlate well.