Analyzing normetabolites of the fentanyls by gas chromatography/electron capture detection

A selective and sensitive gas-liquid chromatographic (GC) method has been developed for analyzing the normetabolites of fentanyl and 3-methylfentanyl in urine. The method employs differential pH extraction of 1 mL samples, extractive acylation with pentafluoropropionic anhydride (PFPA), GC separation on a fused-silica capillary column (DB-1701), and detection by electron capture detector (ECD) or mass spectroscopy (MS). Limit of sensitivity for this method is 2 ng/mL for norfentanyl (NF) and nor-3-methylfentanyl (N-3-MF) using a 1-mL urine sample and a 2-microL injection from a final volume of 20 microL. Within-run precision, expressed as the coefficient of variation (CV), was 14% and 5% for 4 ng/mL and 16 ng/mL of NF and 9% and 4% for the same concentrations of N-3-MF. Between-run precision was 30% and 12% for NF and 11% and 10% for N-3-MF, at 4 ng/mL and 16 ng/mL, respectively. Metabolites are stable in urine for at least one month at room temperature (25 degrees C) or -20 degrees C. PFP-derivatives of the metabolites were confirmed by high-resolution MS in the electron-impact mode. Three characteristic ions for each metabolite were identified-m/z 392 (molecular ion), m/z 336 (loss of propionyl), and m/z 244 (loss of propionanilide) for N-3-MF-PFP and m/z 378 (molecular ion), m/z 322 (loss of propionyl), and m/z 230 (loss of propionanilide) for NF-PFP, suitable for use in GC/MS with selected ion monitoring as a complimentary confirming technique. This method was validated by analyzing urine samples from individuals suspected of using fentanyl or 3-methylfentanyl.(ABSTRACT TRUNCATED AT 250 WORDS)