Determination of 3-(5-tetrazolyl) thioxanthone 10,10-dioxide in human plasma, urine and faeces

A gas chromatographic method is described for assay of 3-(5-tetrazolyl) thioxanthone 10,10-dioxide (BW 59C) in human plasma, urine and faeces. After extraction into 1,2-dichloroethane from alkaline medium the compound is converted to the heptafluorobutyrate derivative which is injected into a gas chromatograph and measured using a 63Ni electron capture detector. The assay produces a linear calibration curve over the range 0-30 mug/ml when the internal standard method is used. Reproducibility is good and sensitivity down to 1 ng injected on column is possible. The method has been used to investigate the pharmacokinetic properties of BW 59C in man and has been semi-automated by the use of an autosampler and dedicated computer.