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Simultaneous determination of codeine and morphine in biological samples by gas chromatography with electron capture detection.

A sensitive gas chromatographic method for the simultaneous determination of codeine and morphine in plasma and brain samples is described. The method involves solvent extraction of the compounds from plasma, derivatization with pentafluoropropionic anhydride and subsequent separation on a 3% OV-17 column. The quantification is performed with electron capture detection. The sensitivity of the method (0.75 ng of morphine and 7.5 ng of codeine in a sample) makes it especially useful for pharmacokinetic investigations. The method was successfully applied to determine the time course of codeine and its metabolite morphine after intravenous administration of codeine to the rat.