Stability of ecgonine methyl ester in postmortem urine specimens

In this study, 25 postmortem urine specimens testing positive, for cocaine and ecogonine methyl ester (EME) by full scan electron impact gas chromatography/mass spectrometry, were used to evaluate the stability of EME in refrigerated and frozen conditions. After an initial quantitation (t = 0), these specimens were split and stored at either 4 degrees C or -20 degrees C. At several intervals, over a six month period, the specimens were tested for cocaine and EME. Twenty-two of the frozen specimens were within 20% of their t = 0 EME concentration after 6 months; 19 of the 25 refrigerated specimens showed similar stability. At least 50% of the EME present was detected in all specimens under both storage conditions. In addition, there was no evidence to suggest that EME concentrations increased over time even though decreases in cocaine concentrations were observed over the same time period. This suggests that the presence of EME in urine specimens indicates in vivo conversion of cocaine and, therefore, use of cocaine.