Direct stopped-flow fluorescence polarization immunoassay of abused drugs and their metabolites in urine.

Kinetic methodology was applied to the direct determination of abused drugs (amphetamines, cocaine, and cannabinoids) in urine by stopped-flow fluorescence polarization immunoassay (SF-FPIA). This technique provides analytical data within a few seconds by measuring the variation of polarized fluorescence with time during development of immunochemical reactions. Methods based on this principle are particularly suitable for routine screening of these drugs in urine, being more expeditious than conventional FPIA methods. The dynamic ranges of the calibration curves were 20-300 micrograms/L for d,l-amphetamine, 15-300 micrograms/L for benzoylecgonine (a cocaine metabolite), and 10-400 micrograms/L for 11-nor-delta 8-tetrahydrocannabinol-9-carboxylic acid (a cannabinoid metabolite). The detection limits and within- and between-assay precision were better than those provided by conventional FPIA. Analytical recoveries ranged between 97.5% for d,l-amphetamine and 102.4% for the cannabinoid metabolite. The results for the three analytes were consistent with those obtained by conventional FPIA.