Gas chromatographic-mass spectrometric quantitation of tri-, di- and monomethylxanthines and uric acids from hepatocyte incubation media.

A gas chromatographic-mass spectrometric method is described for the measurement of the concentration of fourteen methylxanthines and methyluric acid metabolites of methylxanthines, especially caffeine, from cell incubation media. The method shows linearity, accuracy and recovery suitable for metabolic studies. The reproducibility of relative retention times is satisfactory (less than 0.07%) and allows rapid and conclusive identification of chromatographic peaks corresponding to metabolites. Moreover, this method enables the simultaneous determination of 3.7-methylxanthine and its 1.7-isomer, which are not chromatographically resolved. This method can be successfully applied when molecules labelled with stable isotopes are used as tracers for metabolic studies.