Limit for qualitative detection of benzoylecgonine in urine using EMIT reagents and the Hitachi 705 automatic...

The limit of detection for the cocaine metabolite (hydrolysis product), benzoylecgonine, using Syva EMIT reagents and the Hitachi 705 automatic analyzer has been found to be 10 ng/mL at the 99% confidence level. For this determination 30 controls were prepared from a single urine pool known to be negative for cocaine metabolite. Urine samples of 90 patients were found to be drug-free when analyzed by selected ion monitoring gas chromatography/mass spectrometry for ecgonine methyl ester and benzoylecgonine at sensitivities of less than 0.4 ng/mL and 1.3 ng/mL, respectively. To test matrix effects on the limit of detection, these samples were screened with the Hitachi 705. Results for eight of the known negative samples fell above the 10-ng/mL limit of detection while only one presumptive positive resulted at an arbitrary 20-ng/mL cutoff. Detection limits were also determined using 20 different negative patients' urine samples fortified with benzoylecgonine. At the 99% confidence level using EMIT d.a.u. and 705 reagents the detection limits were found to be 44 ng/mL and 35 ng/mL, respectively. It was found that 62% of patients' samples positive for benzoylecgonine fell below the 300-ng/mL cutoff and above a cutoff at 50 ng/mL.