“…As far as the time used to carry out this methodology, the method described here can be considered an intermediate one between very rapid methods developed to measure only caffeine and dimethylxanthines (Aramaki et al, 1991;Tanimura, 1994), and those for all caffeine metabolites found in mammalians and humans, including methylxanthines and methyluric acids (Lelo et al, 1989;Berthou et al, 1989) which take two to three times longer to run than our new method. Methylxanthine standards (1 : 7-methylxanthine; 2: 3methylxanthine; 3: 1 -methylxanthine; 4: 3,7-dimethylxanthine; 5: 1,7-dimethylxanthine; 6: 1,3-dimethyIxanthine; 7: Internal Standard; 8: 1,3,7-trimethyIxanthine).…”