Isocaffeine ; Caffeine monohydrate - Impurity C (EP); 1,3,9-Trimethyl-3,9-dihydro-1H-purine-2,6-dione; 3,9-Dihydro-1,3,9-trimethyl-1H-purine-2,6-dione; 1,3,9-Trimethylxanthine;9-Methyltheophylline ; Caffeine Related Compound C; Caffeine EP Impurity C ;