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

Vitamin B12 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 B12, 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 B12 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 B12 was obtained by square wave voltammetry at pH 10.0. It was found to be linear from 0.25 to 5.0 μmol 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 B12 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.