Methadone conversion to EDDP during GC-MS analysis of urine samples

During validation of a gas chromatography-mass spectrometry (GC-MS) method for the methadone metabolite 2-ethylidine-1,5dimethyl-3,3-diphenylpyrrolidine (EDDP), it was noted that detectable levels of EDDP were found during analysis of extracts from drug-free urine samples spiked with methadone. Different amounts of EDDP were detected by GC-MS during confirmation analysis; however, levels consistently exceeded 50 ng/mL at methadone concentrations > 10,000 ng/mL. Quantitation of EDDP was determined by the addition of EDDP-d3 to methadone-spiked urine samples. Subsequent analysis of methadone-spiked urine extracts by high-performance liquid chromatography (HPLC) indicated no EDDP as a result of contaminated standard or conversion during solid-phase extraction. Reducing the GC injector-port temperature from 260 degrees C to 180 degrees C reduced the observed EDDP concentration in one sample from 201 ng/mL to 53 ng/mL at the initial methadone concentration of 10,000 ng/mL. These results indicate GC injector-port temperature induces thermal conversion of methadone to EDDP as an artifact. When confirmation of methadone and EDDP is critical to determining individual compliance with maintenance programs, alternative chromatographic methods (e.g., capillary electrophoresis, HPLC, or liquid chromatography-mass spectrometry) should be considered.