A novel electrochemical strategy for determination of vitamin B12 by Co(I/II) redox pair monitoring with boron-doped diamond electrode

Vitamin B-12 supplementation is recommended mainly for people who are vegetarian or vegan. The wide extent of the use of this supplementation should act as a warning sign regarding the quality of commercially available products. In this context, a novel electrochemical strategy is proposed for the determination of vitamin B-12, where the Co(I/II) redox pair is monitored using a boron-doped diamond electrode for the analysis of supplementation products. The surface of the boron-doped diamond was characterized by electrochemical impedance spectroscopy and cyclic voltammetry. The electrical properties of the electrode are highly influenced by its surface terminations and a cathodic pretreatment of -2.0 V for 30 s in 0.5 mol L-1 H2SO4 before the analysis enhanced the analytical response. The cyclic voltammograms for vitamin B-12 obtained at pH 5.0 showed four peaks: two oxidation peaks at -0.74 and + 0.18 V, corresponding to Co(I/II) and Co(II/III) oxidations, respectively, and two reduction peaks at -0.12 and -0.75 V, corresponding to Co(III/II) and Co(II/I) reductions, respectively. The experimental parameters (pH, supporting electrolyte, pulse technique) were optimized for the monitoring of the Co(I/II) redox pair. The calibration plot for vitamin B-12 was obtained by square wave voltammetry at pH 10.0. It was found to be linear from 0.25 to 5.0 mu mol L-1, with a detection limit of 86.0 nmol L-1. A boron-doped diamond electrode with cathodic pretreatment was employed to determine vitamin B-12 levels in fortified toothpaste and supplementation tablets. The results were compared with those provided by UV-vis spectrometry. The statistical analysis showed no significant difference between the two methodologies in terms of the precision and accuracy of the data obtained.