New gas chromatogrphic assay for the quantification of methadone. Application in human and animal studies

A new gas chromatographic assay utilizing 2-dimethylamino-4,4-diphenyl-5-nonanone as the internal standard was developed for the quantification of methadone. The method involved extraction of methadone with 1-chlorobutane from tissue at pH 9.8, re-extraction of an aliquot of the organic solvent with 0.5 M sulphuric acid, alkalinization and final extraction into chloroform. The assay was used to determine the concentration of methadone (i) in whole blood samples from a normal volunteer following a single 9.4-mg oral dose of d-methadone hydrochloride, (ii) in whole blood, saliva and gastric juice from a methadone addict maintained on 90 mg of dimethadone hydrochloride per day, (iii) in mouse liver microsomes incubated with methadone, and (iv) in the perfusate of the isolated perfused rat liver.