GLC method for the quantification of metabolites of thymoxamine in human plasma

A sensitive gas-chromatographic method for quantification of the pharmacologically active metabolites I-IV of thymoxamine in plasma is described. 4-(Hydroxythymyl)-(2'methylbutylaminoethyl)ether, a compound similar to metabolite I, is used as an internal standard. Metabolites I and II the internal standard are extracted with cyclohexane from alkalinized plasma followed by back-extraction into 0.1 N hydrochloric acid. After evaporating the hydrochloric acid solution, the sample is silylated with BSTFA and analyzed by gas-chromatography on a CRS 101/Carbowax 4000 column using a thermoionic detector. For subsequent determination of metabolites III and IV, the extracted plasma is hydrolyzed under conditions in which the phenol sulfates but not the glucuronide conjugates undergo cleavage. The resulting phenols (metabolite I and II) are analyzed as described above. The sensitivity threshold for all 4 compounds is approximately 5 ng/ml plasma based on a 2 ml plasma sample.