Spectroelectrochemical Study And CE-ECL Determination Of Catechin

As a representative of a large family of flavonol compounds, catechins are particularly attracted attention because of their relative high antioxidant capacity. Catechins are widely distributed in teas, and plants. There are growing evidences that catechins are efficient free-radical scavengers and possess the inhibitory effect on human plasma oxidations and cancers , etc. The present work studied the electrochemistry behaviors of catechin on graphite-wax paste electrode (GWE), in Britton-Robinson buffer solutions involving 0.5 mol·L^-1 KCl as supporting electrolyte, using cyclic voltammetry and differential pulse voltammetry and the in situ thin layer spectroelectrochemistry. And, a method of capillary electrophoresis (CE) with Luminol-electrogenerated chemiluminescence (ECL) detection which based on the enhancement effect of catechin on the chemiluminescence of luminal system has been developed for the determination of catechin.The results indicate that GWE displayed great power to adsorb catechin. The oxidation of o-dihydroxy groups at B-ring occurred firstly in the lowest potentials and was a highly reversible reaction involving 2-electrons and 2-protons. The second oxidation in relatively positive potentials probably corresponded to the transformation between 7-OH group at A-ring and 7-position oxygen free radical. GWE shows good data stability. Differential pulse voltammetry indicates that there is a good linear relationship between the main oxidation peak current of catechin which indicates that GWE can be used in electroanalysis of catechin.Cyclic voltammetry and thin layer spectroelectrochemistry test results indicate that the adsorption and oxidation of catechin on a GWE in a longoptical-path thin-layer electrochemical cell. The characteristic bands of catechin showed potential-dependent variations under controlled-potential oxidation. And, cyclic voltabsorptiograms (CVAs) were recorded in different potential ranges for catechin, at characteristic wavelengths of species. The derivative cyclic voltabsorptiograms (DCVAs) were analysed for reconstruction of cyclic voltammograms (CVs) of these species appeared in the solution during electrolysis using self-developed computer programs. The results indicate that the first oxidation step of catechin is an adsorption-controlled reaction, in which the total current is mostly contributed from the adsorbed species.The effects of pH on the autoxidation and electroxidation of catechin were studied by the CVAs. The results show that the oxidation of catechin can be accelerated by pH increased; Its characteristic wavelength is redshift with increasing pH ; In extended to the visible wavelength range of products have a wide overlap absorption bands; The solution color changed from colorless to yellow. At the same time, the contribution of both the species in solution and those pre-adsorbed on the electrode surface to the total redox currents can be estimated under different pH conditions. The result shows that the oxidation process of catechin is controlled by the adsorption once again. Moreover, the adsorption of catechin on the electrode surface is weakened with increasing pH. It proved that there was strong absorption of catechin in the acidic conditions, and had a good shape.A method of capillary electrophoresis (CE) with Luminol-electrogenerated chemiluminescence (ECL) detection has been developed for the determination of catechin. Separation column was a 25μm i.d. capillary. The running buffer was 50 mmol/L boric acid + 25 mmol/L potassium dihydrogen-phosphate buffer (pH = 8.0). The solution in the detection cell was 1.0 mmol/L Luminol + 0.3 mol/L KCl (pH 10.5). Other optimized conditions comprise electrokinetic injection at 16 kV for 10 s, seperation voltage at 12 kV and detection potential at 0.6 V. A linear relation between ECL intensity and catechin concentration was obtained in the range of 8.0×10^-6 -1.0×10^-3 mol/L, with a detection limit of 1.0×10^-6 mol/L. The relative standard deviations (n = 5) of migration time and ECL intensity were 0.64% and 4.1%, respectively, for the detection of 1.0×10^-3 mol/L catechin. The method was successfully applied to the determination of catechin in catechu with satisfactory result.