Determination of codeine and metabolites in plasma and urine using ion-pair high-performance liquid chromatography

A reversed-phase ion-pair high-performance liquid chromatographic method for the simultaneous determination of codeine and seven metabolites is described. The samples are purified by reversed-phase solid-phase extraction. Codeine, norcodeine, codeine-6-glucuronide, norcodeine-6-glucuronide and morphine-3-glucuronide are measured with UV detection. Detection limits are 3 nmol/l (morphine-3-glucuronide) to 20 nmol/l (codeine). Morphine, normorphine and morphine-6-glucuronide are measured with electrochemical detection. Detection limits are 0.4 nmol/1 (morphine-6-glucuronide) to 1.0 nmol/l (normorphine). Correlation coefficients better than 0.998 are normally obtained for all compounds. The method was applied to the determination of the kinetics of codeine and its metabolites in plasma and urine samples from healthy volunteers.