J. Vasiliades
Jul 1, 1993
Citations
0
Influential Citations
18
Citations
Journal
Journal of analytical toxicology
Abstract
To the Editor: In a previous communication, we presented a simple, sensitive, and selective quantitative procedure for ecgonine methyl ester (EME) analysis in urine (1). The between-run precision of this assay was 10%. Using the above procedure we evaluated the long term stability of EME in urine. Ecgonine methyl ester hydrochloride was purchased from Sigma Chemical Co. (St. Louis, MO). Drug free urine was spiked with a known concentration of EME (0.84 mg/mL). The pH was adjusted with sodium hydroxide or hydrochloric acid, and the three urines, pH 3, 5, and 9, were analyzed on the day of sample preparation. Samples were stored in a refrigerator at 4-5~ between analyses. At known time intervals, the samples were taken from the refrigerator and analyzed using our previously described procedure (1). Results, which are reported as percent loss from the day of sample preparation, were calculated using the pH 5 urine as standard. Three years later, the three samples at pH 3, 5, and 9 were analyzed for the presence of EME. For the three-year stability determination, an EME standard was prepared in fresh drug-free urine and was used to calculate the EME concentration in the pH 3 and 5 samples. Table I shows the results of samples that were analyzed for the presence of EME at pH 9 and 3 over a Table I. Ecgonine Methyl Eater Stability In Urine 29-day period, and three years later at pH 3, 5, and 9. EME was unstable under basic conditions, pH 9, with % EME loss* against pH 5.0 standard 100% of the EME being lost in 30 days. Similar results Time pH 5.0