Methyl xanthine analysis

Fig. 11.8. Analysis of theophylline in the presence of caffeine and its metabolites1 Precolumn Lichrosorb RP2 (45x2.0 mm ID), column Ultrasphere ODS 5 urn (150x4.6 mm ID), mobile phase 0.01 M sodium acetate and 0.005 M tetrabutylammonium hydrogen sulfate in water (pH 4.75 with 0.1 M acetic acid or sodium hydroxide) to which 12.5% methanol is added, flow rate 1.5 ml/min, detection UV 274 nm. Peaks 1, uric acid 2, 3-methyl xanthine 3, 1-methylxanthine ...

Cyclic AMP phosphodiesterase inhibitors, with or without an appropriate agonist are also candidates for clinical experimentation. In preliminary work, which requires confirmation, we have reported greater low Km cyclic AMP phosphodiesterase activity in psoriatic lesions than in normal appearing areas in six patients. If this is the case in an in vivo lesion and is not an artifact of tissue preparation for biochemical analysis, a cyclic AMP phosphodiesterase inhibitor may be an excellent choice. We have shown that epidermal cyclic AMP phosphodiesterase is inhibited by caffeine, theophylline, diazepam, papaverine and R020-1724. The methyl xanthines are poor inhibitors, whereas papaverine and R020-1724 are potent... 

Methyl xanthines in tea extracts have been widely analyzed using reversed-phase Cjg column with UV detection. They have absorption maxima at 210 and 274 nm, the latter being more often reported as it is more specihc. HPLC conditions employed varied according to the level of interferences in the extracts. Fernandez et al. reported simultaneous analysis of five catechins and three methyl xanthines by RP-18 HPLC. Without pretreatment of samples, complete separation was achieved in 18 minutes using a gradient mobile phase of water-formic acid-acetonitrile. Iso-cratic elution with methanol-0.1% ortho-phosphoric acid (20 79.9 0.1, v/v) for the analysis of the same components required 60 minutes. Such time-consuming... 

Nakakuki, H., Horie, H., Yamauchi, Y., and Kohata, K. 1999. Rapid analysis of methylated xanthines in teas by an improved high-performance liquid chromatographic method using a polyvinylpolypyrroridone pre-column. J. Chromatogr. A 848 523-27. 

Liquid chromatographic analysis of free purine and pyrimidine bases can be carried out on either cation-exchange or reversed-phase columns. The separation of a mixture of 10 methylated xanthines has been accomplished using reversed-phase LC on a column of Apex Octadenyl 3 pm kept at 50°C, in less than 2 min. This mixture included caffeine, theophylline, and theobromine, which are very important compounds in the food and pharmaceutical industries. 

From metabolic studies, an isotopic caffeine breath test has been developed that detects impaired liver function using the quantitative formation of labeled carbon dioxide as an index. From the urinary excretion of an acetylated uracil metabolite, human acet-ylator phenotype can be easily identified and the analysis of the ratio of the urinary concentrations of other metabolites represents a sensitive test to determine the hepatic enzymatic activities of xanthine oxidase and microsomal 3-methyl demethylation, 7-methyl demethylation, and 8-hydroxylation. Quantitative analyses of paraxanthine urinary metabolites may be used as a biomarker of caffeine intake. Fecal excretion is a minor elimination route, with recovery of only 2-5% of the ingested dose. 

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