Extraction of methylxanthines from human body fluids by solid-phase microextraction Original Research Article

Four methylxanthines, caffeine, theobromine, paraxanthine and theophylline, have been found extractable from human whole blood and urine samples by solid-phase microextraction (SPME) with a Carbowax/divinylbenzene-coated fiber. Their determination was made by using capillary gas chromatography with nitrogen phosphorus detection. Extraction efficiency of the methylxanthines was 0.01–0.047% for whole blood, and 0.05–0.229% for urine, respectively. The regression equations for the compounds showed excellent linearity in the range 1.88–60 μg ml−1 for whole blood and urine samples, except for caffeine (0.31—-20 μg ml−1 for whole blood and 0.16–20 μg ml−1 for urine). The detection limits for each of the compounds were 0.2–0.9 and 0.06–0.7 μg ml−1 for whole blood and urine, respectively. The coefficients of within-day variation in terms of extraction efficiency for all compounds in whole blood and urine samples were 3.2–9.3% and 2.6–8.4%, respectively. The data obtained for the actual determination of four methylxanthines in a male subject after ingestion of coffee or cocoa were also presented.