Direct voltammetry for vitamin B(2) determination in aqueous solution by using glassy carbon electrode

Application of renewable silver amalgam annular band electrode to voltammetric determination of vitamins C, B1 and B2

In this work, the design and results of applying silver liquid amalgam film-modified silver solid amalgam annular band electrode (AgLAF-AgSAE), refreshed before each measurement, to voltammetric determination of vitamins C (VC), B(1) (VB1) and B(2) (VB2) are presented. The method is based on adsorptive accumulation of analytes at the AgLAF-AgSAE in a phosphate buffer (VB1), phosphate buffer with Triton X-100 (VB2) and an alkaline borate buffer with Triton X-100 (VC). The analytical parameters and procedure of electrode activation were optimized. The calibration graphs obtained for vitamins C, B(1) and B(2) are linear, respectively, for concentration range 0.05-12, 0.01-0.1 and 0.05-3 mg L(-1). The detection limits were calculated and equaled 0.02, 0.003 and 0.009 mg L(-1), while repeatability of the peak current was 2%, 1% and 3%, respectively. These results are comparable with results obtained for polarographic determination of the same vitamins using mercury electrodes. Finally, the AgLAF-AgSAE was applied to the determination of vitamins in pharmaceutical samples and fruit juices with satisfactory results.

A new approach to the rest potential of biological membranes

In a series of recent papers, Bonciocat et al., have shown that the faradaic current density of an electrode redox reactions occurring with combined limitations, of charge transfer and nonstationary linear, semi-infinite diffusion, is the solution of an integral equation of Volterra type. This integral equation has been transformed to describe the transport of ions through the interface between two immiscible electrolytic solutions. According to Goldman, Hodkin, Katz theory, the rest potential of a biological membrane is determined by the maintenance of different concentrations of the ions Na+, K+ and Cl-, in the two aqueous solutions separated by the membrane. Using the integral equations (of Volterra type) for the ionic current densities iNa, iK, iCl, and applying the open circuit condition (i.e., iNa + iK + iCl = 0), the potential differences at the junctions: aqueous solution (I)/membrane, respective membrane/aqueous solution (II), have been obtained. To get the diffusion potential across the membrane, the Planck's theory has been used. The sum of these three contributions gives the expression of the rest potential (and a comparison with the Goldman-Hodkin-Katz formula is made, showing in what conditions they become identical formulae).