Determination of codeine in human plasma by high-performance liquid chromatography with fluorescence detection.

A rapid, reliable and rugged assay for determining codeine in human plasma using reversed-phase high-performance liquid chromatography with fluorescence detection was developed. This analytical method utilized an ion-exchange/mixed-mode solid-phase extraction procedure. The chromatographic separation was achieved using a 150 x 4.6 mm I.D., 3-microns reversed-phase C8 (deactivated for basic analytes) column at ambient temperature. Fluorescence detection (excitation at 214 nm and emission above 345 nm) for codeine and nalorphine allowed for a detectable limit of 5 ng/ml. The results showed that the method was linear from 10 to 300 ng/ml. The method had good reproducibility, precision, accuracy and recoveries of 91 and 90% for codeine and nalorphine, respectively. This method has been applied to study the pharmacokinetics of codeine in normal human subjects.