Simultaneous determination of fenfluramine and phentermine in urine using gas chromatography mass spectrometry with pentafluoropropionic anhydride derivatization

Fenfluramine and phentermine ('fen-phen') are stimulants used primarily for weight loss that have a causative association with serious health problems. Though voluntarily removed from the market by their manufacturers and the FDA in September of 1997, both drugs occasionally reappear in the clinical and forensic setting from individuals who retained old prescriptions, transported the drugs from foreign countries, or 'stockpiled' the medications immediately before their removal from the market. The authors describe an analytical method for simultaneous detection of fenfluramine, phentermine, and the internal standard, N-propylamphetamine, in urine using pentafluoropropionic anhydride derivatization. Detection using and mass spectrometry is described. Baseline resolution of the analytes was achieved in the presence of four other common sympathomimetic amines. The increased molecular weights, better peak profiles, and characteristic fragments containing portions of both derivatizing agent and parent compound aid in the unambiguous identification of these analytes.