Determination of methadone and its primary metabolite in human urine by capillary electrophoretic techniques

Data presented in this paper show that methadone and its primary urinary metabolite (M1) can not easily be determined by SDS-based micellar electrokinetic chromatography; however, they separate rapidly under cationic capillary zone electrophoretic conditions using a borate buffer with a pH of ca. 9. Eight urines obtained from individuals undergoing methadone therapy, which tested markedly positive for methadone using an enzyme multiplied immunoassay and in which the presence of methadone and M1 was also confirmed by GC-MS, have been analyzed. Using an extraction procedure with disposable cartridges containing a copolymeric sorbent, the presence of methadone and M1 could be confirmed in all urines, whereas with direct urine injection, the two compounds could only be determined in six urines. Thus, for unambiguous confirmation by capillary electrophoresis, extraction of the compounds of interest is preferred. The described assay is rapid (with typical run times being less than 6 min), free of interferences from coextracting drugs of abuse and/or their major metabolites, and characterized by a good reproducibility. After extraction of 5 ml urine, drug concentrations down to ca. 20 ng/ml can be monitored unambiguously.