Determination of methadone and its metabolites EDDP and EMDP in human hair by headspace solid-phase microextraction and gas chromatography–mass spectrometry

Abstract

A simple method for analysis of methadone and its two main metabolites EDDP and EMDP in hair was developed using automatic headspace solid-phase microextraction (HS-SPME) at a multipurpose sampler and gas chromatography – mass spectrometry with electron impact ionization and selected ion monitoring (GC–MS-SIM). The washed hair pieces were digested in the closed headspace vial in 1 ml 1 M NaOH containing 0.5 g NaCl and each 10 ng of the internal standards D 9-methadone and D 3-EDDP at 110°C for 20 min. Then the HS-SPME was performed with a 65 μm polydimethylsiloxan/divinylbenzene fiber at the same temperature in the same vial for another 20 min followed by the desorption in the GC injection port. The calibration curves were linear between 0.1 and 3 ng/mg (methadone and EMDP) and 10 ng/mg (EDDP) respectively, at higher concentrations a negative deviation from linearity was found. The detection limits were 0.03 ng/mg (methadone) and 0.05 ng/mg (EDDP and EMDP), and the reproducibility was 9.2% for methadone and 11.2% for EDDP ( n=12). The method was applied to hair samples of 26 drug fatalities. 19 cases were positive with 0.36–11.8 ng/mg methadone and 0.19 –10.8 ng/mg EDDP. EMDP was found only in two cases with 0.18 and 0.84 ng/mg. The methadone concentration range was in agreement with previous data, but the EDDP/methadone concentration ratios (0.19–0.67) were definitely higher than those determined by other methods.