Electrochemical detection of lipophilic antioxidants with high sensitivity at boron-doped diamond electrode

The electrochemical detection of lipophilic antioxidants, α-tocopherol (vitamin E, VE) and ubiquinone (coenzyme Q10, CoQ10), in methanol and in methanol/hexane mixture solutions, respectively, at boron-doped diamond (BDD) electrodes was investigated by cyclic voltammetry (CV) and flow-injection electrochemical measurements. CV measurements revealed that the overpotential for electrochemical reaction of VE and CoQ10 was larger at an oxidized BDD electrode surface than at that of a hydrogenated BDD (H-BDD) electrode. The slope of the CV calibration curve used to determine the VE and CoQ10 concentrations was larger at a glassy carbon (GC) electrode than at the H-BDD electrode; however, the signal-to-background ratio was larger at the H-BDD electrode than at the GC electrode, due to the low background feature of the H-BDD electrode. The limit of detection (LOD), defined by a signal-to-noise ratio of three for flow-injection electrochemical detection, was much smaller at the H-BDD electrode (VE: 41 nM and CoQ10: 17 nM) than at the GC electrode (VE: 263 nM and CoQ10: 71 nM). These results confirm that the H-BDD electrode is reliable for the electrochemical detection of lipophilic antioxidants, especially at low concentrations.