Study on the adsorptive catalytic voltammetry of emodin at a carbon paste electrode

An extremely sensitive catalytic voltammetric peak of Emodin at 20.59 V ( vs. SCE) was obtained in 0.40 M NH4Cl-NH3 center dot H2O buffer (pH 8.2) in the presence of dissolved oxygen at a carbon paste electrode (CPE). The experimental results showed that Emodin was efficiently accumulated at a CPE by adsorption. In the following potential scan, Emodin was reduced to homologous anthrahydroquinone compound, then the compound was immediately oxidized to Emodin by the dissolved oxygen in the solution, and the Emodin was again reduced at the CPE. As a result, a cyclic catalytic reaction was established. At the optimal conditions, the peak current is linearly proportional to the Emodin concentration in the range of 3.0 x 10(-10) M similar to 4.0 similar to 10(-9) M (accumulation 70 s) and 4.0 x 10(-9) M similar to 4.0 x 10(-8) M (accumulation 30 s). The detection limit is 1.0 x 10(-10) M for a 90 s accumulation. The proposed method was successfully applied to determine Emodin in Polygonum multiflorum Thunb. The results are consistent with results obtained by HPLC.