Electrochemical Sensor for Caffeine Based on a Glassy Carbon Electrode Modified with an Attapulgite/Nafion Film

In the present work, a simple and economic analytical method based on attapulgite/nafion coated glassy carbon electrode (AT/Naf/GCE) has been developped for the electrochemical determination of caffeine. Prior to its use, the ionic exchange properties and conductivity of AT/Naf/GCE were studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Caffeine gave an irreversible oxidation peak around +1.41 V (vs Ag/AgCl reference electrode) in 0.1 M H₂SO₄ at pH 1.5. The peak current varied linearly with the square root of the scan rate, showing that the transfer process is controlled by diffusion. The heterogeneous rate constant, the transfer coefficient and the number of electrons involved were calculated. Upon optimization of key analytical parameters involved in the electroanalysis of caffeine by DPV, the recorded oxidation peak current varied linearly with caffeine concentration in the range from 0.1 to 4 μm, leading to a detection limit of 4.57×10^?8 M (S/N=3). The developed electrode exhibited good stability and was easily regenerated. The effect of some important potential interfering compounds (ascorbic acid, dopamine, uric acid, sulphite ions and glucose) on the signal of caffeine was also examined. The obtained electrode was successfully employed in the determination of caffeine content in a commercial drug.