Voltammetric determination of caffeine in beverages using a chemically modified electrode

A Nafion-ruthenium oxide pyrochlore chemically modified electrode is used for the determination of caffeine in beverages by square-wave voltammetry. Compared to a bare glassy carbon electrode, the chemically modified electrode exhibits a marked enhancement of the current response. A linear calibration curve is obtained over the 5-200 mu M range in 0.05 M HClO4 solution with a detection limit (3 sigma) of 2 mu M. The results of 15 successive repetitive measurement-regeneration cycles showed a relative standard deviation of 2.7% for 10 mu M caffeine. Thus, the electrode renewal gives a good reproducible surface. Quantitative analysis was performed by the standard addition method for caffeine content in tea, coffee, decaffeinated coffee, and cola beverages.