Caffeine determination was performed in a Merck LaChrom L-7110 liquid chromatograph equipped with a L-7400 Merck Hitachi UV detector. The detector signal was recorded on a D-7500 Merck Hitachi integrator. The column was an Aquasil C18, 5mm, 4.6200mm with Aquasil C18 SecurityGuard column 104/4.6mm (Thermo Electron, UK).