Urine concentrations of ecgonine from specimens with low benzoylecgonine levels using a new ecgonine assay

A new approach to detecting drug positives for cocaine in urine having benzoylecgonine concentrations below the Department of Defense (DoD) cutoffs was examined by measuring the concentrations of the metabolite ecgonine. The DoD cutoff concentrations for determining a positive for cocaine are 150 and 100 ng/mL for radioimmunoassay and gas chromatography-mass spectrometry, respectively. To facilitate this approach, a new assay was developed for ecgonine using only 1 mL urine. The urine was passed through an anion-exchange cartridge, and the eluant was evaporated to dryness in a water bath under nitrogen. The residue was subjected to nonylation and a standard back extraction procedure before a second derivatization with propionic anhydride. A total of 139 urine specimens were analyzed in this manner, and 104 yielded ecgonine concentrations greater than 50 ng/mL. The average ecgonine concentration in the latter specimens was approximately 5 times the comparable benzoylecgonine concentration. By monitoring ecgonine alone or in conjunction with benzoylecgonine, the number of cocaine positives detected in urine could be dramatically increased.