On-line electrochemistry-liquid chromatography with UV absorbance detection for elucidating the electrochemical oxidation mechanism of α-tocopherol in methanol

Electrochemical studies of α-tocopherol were carried out in methanol-acetate buffer solution. α-Tocopherol displayed one anodic peak in a cyclic voltammogram. Two-electron transfer in the oxidation of α-tocopherol was demonstrated by coulometry. The on-line electrochemistry-liquid chromatography with UV absorbance detection method was developed to separate and detect the intermediates and products which were formed during the oxidation of α-tocopherol. When the potential was controlled at +0.8 V (vs. Pd), the intermediates 9-hydroxy-α-tocopherone and 9-methoxy-α-tocopherone were identified together with the ultimate α-tocopherylquinone product. Intermediates and products formed in the chemical oxidation of α tocopherol by N-bromosuccinimide were also studied. The changes in the Chromatographie peaks indicated a clear transformation of 9-hydroxy-α-tocopherone into the quinone. The experimental results revealed that the intermediates and products generated in the electrochemical and chemical oxidation processes were essentially the same.