STEREOSELECTIVE DETERMINATION OF METHADONE IN SERUM BY HPLC FOLLOWINGSOLID-PHASE EXTRACTION ON DISK

A solid-phase extraction (SPE) technique for methadone has been develo ped using a mixed-mode solid-phase extraction disk which contains both hydrophobic and cation-exchange functional groups. The SPE technique was used to isolate the drug from the biological matrix and to prepare a cleaner sample prior to stereoselective analysis by HPLC on a silic a column with covalently bound alpha(1)-acid glycoprotein (Chiral-AGP) followed by ultraviolet detection at 205 nm. The within-run precision was less than 5% for the complete method over the therapeutic range. The quantification limit was 25 ng ml(-1). The between-run precision w as less than 15% at the quantification limit. The between-run precisio n at other concentrations was less than 8.5% with an accuracy of more than 95%. The mean recovery for R-methadone was 78.5% and the mean rec overy for S-methadone was 73.4%. The complete procedure has been valid ated. This method was successfully used for the analysis of 15 clinica l cases.