Adsorptive stripping voltammetric method for the determination of caffeine at integrated three-electrode screen-printed sensor with carbon/carbon nanofibers working electrode

A commercially available screen-printed carbon electrode coated with carbon nanofibers (SPCE/CNFs) and differential-pulse adsorptive stripping voltammetry (DPAdSV) were used to determination of caffeine. The process of electrochemical oxidation of caffeine in 0.1mol L-1 sulfuric acid at the SPCE/CNFs surface was investigated by cyclic voltammetry (CV). The effect of the supporting electrolyte type, pH and concentration, time and potential of accumulation, amplitude and scan rate were studied to select the optimum experimental conditions. Under the optimized conditions, the well-defined caffeine peak was observed at 1.25 V (vs. screen-printed silver reference electrode) in 0.1 mol L-1 sulfuric acid. The caffeine was accumulated at -0.8 V for 60 s. The oxidation peak current was proportional to concentration of caffeine from 2.0 x 10(-7) to 1.0 x 10(-6) mol L-1 with detection limit of 5.6 x 10(-8) mol L-1. The presented method has been successfully applied for the determination of caffeine in beverage samples.