[Determination of methadone in plasma using high pressure liquid chromatography methods].

High-performance liquid chromatography on the column of LiChrosorb RP-18 was applied to the determination of methadone in plasma, after previous precipitation of proteins with methanol and extraction from alkalized plasma with diethyl ether. Methadone, ion-paired with pentane-1-sulphonic acid added in a mobile phase acetonitrile-methanol-ammonium acetate solution (20:58:22), was monitored at 254 nm. Piritramide was used as an internal standard. The determination range was 0.25-1.25 micrograms/cm3 of plasma and recovery was 88-93%.