Determination of Caffeine Using a Simple Graphite Pencil Electrode with Square-Wave Anodic Stripping Voltammetry

Abstract.

A simple commercial graphite pencil electrode (GPE) was utilized for monitoring caffeine using the square-wave anodic stripping voltammetry (SWASV) method. This method was applied to determine the caffeine levels in several tea samples, which yielded a relative error of 1% in the concentrations. Caffeine was deposited at 0.0 V (vs. Ag/AgCl), then reduced at +1.40 V to strip it on the GPE. Optimal experimental conditions for the analysis were found to be as follows: pH value of 9 for the medium; deposition potential of 0.0 V; deposition time of 120 s; SW frequency of 25 Hz; SW amplitude of 45 mV, and step potential of 6 mV. Given these optimum conditions, a linear range was observed within the concentration of 0 ∼ 500 mg L⁻¹. At caffeine concentrations of 50.0, 250.0, and 500.0 mg L⁻¹, the relative standard deviations in measured concentrations (n = 12) were 0.19, 0.09, and 0.11%, respectively. The detection limit was found to be 9.2 mg L⁻¹, which is comparable with the result obtained using a carbon paste electrode, equivalent to 8.2 mg L⁻¹.