Bentonite-modified glassy carbon electrode for the voltammetric determination of caffeine in beverages

This study introduces a glassy carbon electrode modified with Na⁺-exchanged bentonite and Nafion for caffeine determination in beverages using differential pulse voltammetry. Bentonite, a high-surface-area clay, enhances caffeine adsorption, while Nafion stabilizes the clay layer and improves interaction through hydrogen bonding and electrostatic mechanisms. The modification is fast and cost-effective. The electrode demonstrated a linear range of 0.25-4.0 μM, with detection and quantification limits of 0.076 μM and 0.25 μM-five times lower than an unmodified electrode. Caffeine metabolites like theobromine and paraxanthine had minimal interference due to the clay's selective affinity. Results from instant coffee, energy drinks, cola, and green tea matched HPLC-UV within 5 %, confirming accuracy. However, caffeine in yerba mate was 30 % higher, likely due to theobromine interference. This method offers a low-cost, highly sensitive alternative for caffeine determination, improving selectivity over conventional electroanalytical approaches.