Elimination of fluconazole interference in gas chromatography/mass spectrometric confirmation of benzoylecgonine, the major metabolite of cocaine using pentafluoropropionyl derivative.

Cocaine is a widely abused drug and causes death from overdose. Benzoylecgonine, the major metabolite of cocaine in urine is usually confirmed after derivatization by gas chromatography/mass spectrometry to demonstrate cocaine abuse. Recently, Wu et al. demonstrated that fluconazole coelutes with benzoylecgonine after conversion to trimethylsilyl analogs and causes false-negative result in the confirmation test. However, fluconazole did not interfere with the screening assay using a enzyme multiplied immunoassay technique. We demonstrated that by converting benzoylecgonine to the corresponding pentafluoropropionyl derivative, the interference of fluconazole can be completely eliminated. The pentafluoropropionyl derivative of benzoylecgonine eluted at 14.7 min while the derivatized fluconazole eluted at 15.6 min. The mass spectral fragmentation pattern of derivatized benzoylecgonine was distinctively different from the mass spectral features of derivatized fluconazole in both electron ionization and chemical ionization mode of operation of mass spectrometers. The quantitation of benzoylecgonine in positive urine specimens has not affected when the specimens were supplemented with 50 micrograms/mL of fluconazole.