Supporting electrolyte

About: Supporting electrolyte is a research topic. Over the lifetime, 5011 publications have been published within this topic receiving 104172 citations.

Voltammetric behaviour of vitamins D2 and D3 at a glassy carbon electrode and their determination in pharmaceutical products by using liquid chromatography with amperometric detection

Abstract: Cyclic voltammetry was used to study the oxidation of vitamin D2(ergocalciferol) and vitamin D3(cholecalciferol) at a planar glassy carbon electrode. The electrode reaction for cholecalciferol was found to be dependent on the apparent pH between 4.95 and 6.10, and pH independent between pH 6.10 and 8.65 when the solutions contained 90% methanol; this suggested a pKa value of 6.10 for vitamin D3. Similar behaviour was exhibited by ergocalciferol, and a pKa value of 6.35 was found. The peak currents for both vitamins were found to be dependent on the methanol concentration of the supporting electrolyte. The peak currents were also found to be dependent on the ionic strength of the acetate buffer (pH 6.0) over the range 0.1–1.0 mol dm–3. Both substances were oxidized in one step, which was found to be an irreversible reaction; the final product for vitamin D2 can undergo absorption at the electrode surface. The parent compounds could be undergoing oxidation at the triene moieties. The optimum mobile phase for liquid chromatography with amperometric detection was found to be 95% methanol–0.05 mol dm–3 acetate buffer (pH 6.0); the detector was operated at a potential of + 1.3 V (versus Ag—AgCl), and a linear response was obtained for vitamin D3 over the range from 10 to 100 ng injected; for vitamin D2 the response was linear from 20 to 200 ng injected. Extracts of pharmaceutical products were separated on reversed-phase columns prior to amperometric detection of the vitamins. Cholecalciferol was successfully determined in a multivitamin table, and ergocalciferol in a multivitamin liquid preparation.

Principle of unchanging total concentration and its implications for modeling unsupported transient voltammetry

Abstract: The advantages and disadvantages of electrochemistry with little or no added supporting electrolyte are reviewed. Analysis of such systems is complicated by the increased importance of the migrational component of transport. Some computations and analyses can be simplified by invoking the principle that for any electrochemical experiment where the diffusivities of all the solute species do not differ significantly from a common value, the total solute concentration remains uniform and constant. This principle, which applies to both transient and steady-state regimes, holds independently of the cell and electrode geometries and is not compromised by migration and/or convection. The only constraint, additional to the assumption of uniform diffusivities, is the obvious one: that the electron-transfer reaction, and any homogeneous reactions that may participate, do not themselves perturb the number of solute particles (molecules and ions) present. Some consequences of the principle are explored, especially relating to three-ion systems. Using the principle, a framework of procedures is derived which may be followed to obtain a solution to many transient voltammetric problems at a macroelectrode when supporting electrolyte is absent.

Aqueous solutions of salts of poly(vinylsulfonic acid)

Abstract: Specific ion effects in solutions of salts of poly(vinyl sulfonic acid) in aqueous univalent supporting electrolyte are described in regard to observations of phase separation, dialysis equilibrium, light scattering, viscosity, and sedimentation. The most complete data have been obtained on two systems, ammonium poly(vinyl sulfonate) in 0.5M NH4Cl and potassium poly(vinyl sulfonate) in 0.5M KCl. Although the distribution of small ions across a semipermeable membrane is not markedly different in the two cases, other thermodynamic properties, the occurrence of phase separation in the KCl solution and its absence with NH4Cl, together with a larger second virial coefficient in the latter case, indicate that NH4Cl is a much better solvent for the corresponding polymer than is KCl. The hydrodynamic measurements concur in showing that the polymer chain configuration is more expanded in the NH4Cl solution. The interrelations among thermodynamic and hydrodynamic properties developed and generally substantiated for solutions of unionized polymers are found to be valid, at least qualitatively, for both these systems. This study also illustrates how the thermodynamic formalism for a two-component system is applicable to three components, two diffusible and one non-diffusible, provided solutions are equilibrated by dialysis against the solvent mixture.