Analytical electrochemistry of vitamin B12 on a bismuth-film electrode surface

Cyclic voltammetry (CV) and square wave adsorptive stripping voltammetry (SWAdSV) were used to investigate the performance of an ex situ plated bismuth-film electrode (BiFE) employed to study the electrochemical behavior and the electroanalytical determination of vitamin B12. Two pH-dependent reversible peaks were observed for the B12r–B12s (Co(II)–Co(I)) couple after pre-concentration of vitamin B12 at −1.2 V for 30 s. An adsorption-controlled reaction rate with one electron involved in the electrochemical step was observed for the mechanism implicated. The calibration curve obtained in a Britton–Robinson solution at pH 12.0 was linear in the concentration range of 0.100–1.000 μmol L−1 (r = 0.9980). The detection limit was found to be 33.1 nmol L−1. The electrode was successfully employed for the determination of vitamin B12 in two pharmaceutical products. The electrode performance was compared with those of modified and unmodified electrodes as well as with the UV–vis spectrophotometric method.