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. Benzoy lecgonine, the major metabolite of cocaine in urine is usually confirm ed after derivatization by gas chromatography/mass spectrometry to dem onstrate cocaine abuse. Recently, Wu et al. demonstrated that fluconaz ole coelutes with benzoylecgonine after conversion to trimethylsilyl a nalogs and causes false-negative result in the confirmation test. Howe ver, fluconazole did not interfere with the screening assay using a en zyme multiplied immunoassay technique. We demonstrated that by convert ing benzoylecgonine to the corresponding pentafluoropropionyl derivati ve, 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 spectra l fragmentation pattern of derivatized benzoylecgonine was distinctive ly different from the mass spectral features of derivatized fluconazol e in both electron ionization and chemical ionization mode of operatio n of mass spectrometers. The quantitation of benzoylecgonine in positi ve urine specimens has not affected when the specimens were supplement ed with 50 mu g/mL of fluconazole.