Single-reagent polarisation fluoroimmunoassay for the cocaine metabolite, benzoylecgonine, in urine.

A polarisation fluoroimmunoassay is described for the detection in urine of benzoylecgonine, the major metabolite of cocaine. The method uses a single reagent comprising sheep anti-benzoylecgonine serum pre-mixed with a fluorescein-labelled benzoylecgonine derivative as tracer. Under the assay conditions the antiserum has equal cross-reactivity with cocaine and the metabolite. The test is performed by the addition of 10 microL of urine to an aliquot of the single reagent, incubation for a few minutes and measurement of fluorescence polarisation. The assay has a positive/negative cut-off level of 1 mg/L benzoylecgonine and results compare favourably with the EMIT-d.a.u.TM (Syva) system.