Sensitive voltammetric approach employing bare boron-doped diamond electrode as a sensor for determination of hydroxocobalamin

Hydroxocobalamin (OH-CBL) is one of the synthetic forms of water-soluble vitamin B12. This form is an efficient anti-anemic tool with a more prolonged effect than more commonly used cyanocobalamin (CN-CBL). Moreover, OH-CBL is employed as a very efficient and non-toxic antidote in case of cyanide poisoning. Many voltammetric studies have been interested in cobalamines’ voltammetric behavior concerning CN-CBL. The present study aims to examine the voltammetric behavior of OH-CBL and propose a simple and rapid method for its determination. Boron-doped diamond electrode (BDDE) was chosen as a working electrode due to its unique electrochemical properties like a wide potential window, stability, or low and stable background.

It was found that OH-CBL provided four anodic signals on BDDE in acidic supporting electrolytes of pH ≤ 3. With increasing the pH value of the supporting media, the number of signals decreased, and only one current response was recorded in the tested alkaline solutions (pH 8-11). On the other hand, one well-developed cathodic signal was observed in the whole tested pH range. The most negatively situated anodic peak was found suitable for analytical purposes due to its position and shape, which was not influenced by other signals. A supporting electrolyte based on 0.1 mol L^-1 H₂SO₄ was chosen for further experiments. A novel voltammetric approach based on differential pulse voltammetry was developed. After optimization of working parameters, it was proved that the combination of BDDE and DPV provided a sensitive analytical tool, which could be demonstrated by obtained statistical parameters, e.g., LOD = 13.2 nmol L^-1. Moreover, the proposed method was successfully applied to analyze vitamin preparations containing OH-CBL.