Determination of methadone in urine using ion trap GC/MS in positive ion chemical ionization mode

Methadone is a potent analgesic and sedative. It is widely used in the treatment of heroin addiction and is often encountered in forensic specimens. In electron impact (EI) gas chromatography/mass spectrometry (GC/MS) mode, methadone produces predominantly a m/z 72 ion, which is not sufficiently characteristic for identification. Determination of the molecular ion, which can be achieved using chemical ionization (CI) provides diagnostic information and better identification of the drug. This paper describes the development of a positive ion CI GC/MS procedure, using a liquid reagent gas and ion trap instrumentation, for the determination of methadone and its metabolites in urine. CI generally produces a single molecular ion spectrum, but optimization of the reagent gas parameters increases the fragmentation of the molecule, allowing determination of ion ratios if required. The procedure is sensitive, diagnostic and is currently in routine use in our laboratory.