Determination of codeine in human plasma by reverse‐phase high‐performance liquid chromatography

A high-performance liquid chromatographic (HPLC) method for the determination of codeine in human plasma is described. The specific, precise, and sensitive method can be used to determine plasma codeine levels after administration of therapeutic doses of codeine. After purification on a C18 extraction column, codeine in the form of hydrochloride is eluted. After addition of the internal standard, the codeine is separated on a reverse-phase C18 column using a slightly alkaline mobile phase and is then determined by UV detection. The analysis takes 3.5 min per run; the limit of detection is ~3 μg/L for a 50-μL loop and 800 μL of plasma. The absolute recovery is 98.4 ± 6.7% (n = 14) in the 10–300-μg/L range. Within the range, the calibration curve is linear.