Determination of [C-13-N-15] labeled methylxanthines by gas chromatography-atomic emission detection (GC-AED) and compound-independent calibration

Compound independent calibration (CIC) can be used to measure stable isotop ically labeled molecules and their metabolites. This study was designed to demonstrate that gas chromatography coupled to atomic emission detection an d CIC are useful analytical tools for the specific and quantitative determi nation of C-13 and N-15 labeled caffeine and its metabolites. These labeled compounds can be measured by monitoring either C-13 or N-15 atomic emissio n lines and using only one calibration function from one of the analytes. T his method can be helpful when it is difficult or impossible to obtain an a uthentic reference material, which is often the case in metabolic studies.