water. A 5.0mL volume of diluted brewed coffee sample was passed through at a flow-rate of 0.5mL/min. The cartridge was washed with 5.0mL of methanol and caffeine was eluted with 25.0mL of methanol. The eluted samples were filtered with 0.2mm syringe filters and injected directly in the chromatograph. Analytical procedure for the determination of caffeine in brewed coffee is shown in Fig. 1b.