Quantitative determination of plasma oxyphenbutazone by gas-liquid chromatography with selective nitrogen detection

A sensitive and specific gas chromatographic method, using the nitrogen-phosphorus detector for the detection and determination of oxyphenbutazone extracted from plasma is described. The method involves extraction and back-extraction steps followed by derivatization of both oxyphenbutazone and the internal standard with trifluoroacetic anhydride. The procedure permits the rapid and specific routine determination of oxyphenbutazone in plasma with a detection limit of 0.5 microgram/ml. The procedure is linear over the range of concentrations encountered after administration of a single oral therapeutic dose. No interference from the biological matrix is apparent. The suitability of the method for the analysis of biological samples was tested by studying the variation with time of oxyphenbutazone plasma concentrations in normal human volunteers over a period of several biological half-lives.