Adsorptive Stripping Voltammetry in Lipophilic Vitamins Determination

The aim of this contribution was to check if adsorptive stripping differential pulse voltammetry (AdSDPV) is suitable tool for sensitive simultenous electrochemical detection of lipophilic vitamins. Retinol (vitamin A1), cholecalciferol (vitamin D3), α-tocopherol (vitamin E) and phylloquinone (vitamin K1) were selected as representatives. All electrochemical measurements were performed in two separate steps due to the lipophilic character of the analytes. In the first step, an accumulation of lipophilic vitamin on the surface of glassy carbon electrode (GCE) was done by immersing working electrode into the aqueous-acetonitrile solutions (50%, v/v) of each vitamin (50.0 μmol.L) at 400 rpm for 5 min. In the second one, differential pulse voltammetry of accumulated vitamins was performed in 0.01 mol.L acetate (pH 4.5) buffer at potential step (Estep) 5 mV, potential of amplitude (Eampl) 25 mV, interval time (t) 0.1 s and scan rate (ν) 50 mV.s . It was observed that electrochemical behaviour of lipophilic vitamins adsorbed on surface of solid GCE in the aqueous electrolyte was very similar to those performed in organic/aqueous electrolyte in literature. Due to reversible electrochemical behaviour of vitamin K1 (phylloquinone/phyllohydroquinone redox couple), it was possible to detect all lipophilic vitamins only in one analysis. Observed values of peak potentials (Ep) were sufficiently different for their recognition which was confirmed by the analysis of real sample. The results obtained in this study showed that simultaneous determination of some lipophilic vitamins is possible requiring further optimization study. For this reason, it is necessary to understand this work as an initial step in simultaneous determination of lipophilic vitamins without application of any chromatographic technique.