Use of solid-phase microextraction (SPME) for the determination of methadone and its main metabolite, EDDP, in plasma by gas chromatography-mass spectrometry

A simple, rapid method for the determination of methadone and its metabolite 2-ethylene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP) in plasma using solid-phase microextraction (SPME) and gas chromatography-mass spectrometry is proposed. A 100-μm polydimethylsiloxane film fiber was exposed by immersion for 30 min in a diluted plasma solution (1:4 with buffer pH 9) containing both compounds and an internal standard (proadifen). Calibration curves were linear over the concentration range 50-2000 ng/mL. The analysis time was 45 min per sample. The determination of methadone and EDDP was subject to no interference. The performance of SPME was compared with that of liquid-liquid extraction, obtaining lower limits of detection for EDDP. The method using the two extraction procedures was applied to 10 plasma samples from methadone-treated patients.