Formation of benzoylecgonine isopropyl ester following solid-phase extraction

In forensic toxicology general alkaline drug screens typically utilize liquid liquid [LLE] or solid phase extraction [SPE] sample preparation techniques. It is expected that different drugs will be detected when a laboratory changes techniques. In this study, when the authors switched from LLE to SPE they were able to detect benzoylecgonine [BE]. Benzoylecgonine isopropyl ester [BEIE] was also detected. Further investigation demonstrated that the BEIE was formed during sample elution with methylene chloride/isopropanol/ammonium hydroxide. BEIE was not detected if methanol/ammonium hydroxide was used as the elution solvent. Analysts should be aware that BEIE is formed in the presence of BE if elution solvents comprise isopropanol and a strong base. Therefore, use of BEIE as an internal standard in such assays will result in inaccurate quantitation of BE.