A rapid method for the determination of blood morphine concentration suitable for use in studies involving acute and chronic pain.

This communication provides an improved sample preparation method for blood morphine concentration determination prior to high-performance liquid chromatography analysis with electrochemical detection. The lower limit of sensitivity is 1 ng/ml of whole blood, and the standard curve is linear to an upper limit of 500 ng/ml. The coefficient of variation of replicate determinations of morphine at concentrations of 10 and 400 ng/ml were 4.7 and 2.5%, respectively. This assay procedure is rapid and accurate and allows the large number of samples (usually 30-40 samples) generated by pharmacokinetic studies in acute and chronic pain to be conveniently analyzed in one day.