Capillary zone electrophoresis in mixed aqueous–organic media: effect of organic solvents on actual ionic mobilities and acidity constants of substituted aromatic acids

摘要: The effect of the composition binary mixtures acetonitrile (ACN) and water (ranging up to 80%, v/v, ACN) on apparent pKa values actual mobilities 26 aromatic substituted benzoic acids is investigated. (non-thermodynamic) are determined potentiometrically (at T=25°C an ionic strength, I, 5 mmol/l). measured by capillary zone electrophoresis (phosphate buffer, pH 7 in water, I=20 mmol/l, T =25.0°C). An increase with increasing concentration ACN found, a magnitude comparable mixed aqueous–methanolic –ethanolic solvents (1.5 2 pK units at 80% ACN). These changes interpreted based theoretical model transfer activity coefficient or medium effect. change only slightly solvent composition, which fair agreement viscosity. It found that Walden's rule (supposing constancy product mobility, μ, viscosity, η) applied for systems investigated series papers dealing aqueous methanol, ethanol, 1-propanol as cosolvent, anions under consideration obeyed within ±20%. extension this (μη0.9=constant) leads products constant +5 −9% over range 60% organic solvent. substituents (methyl, nitro, chloro, hydroxy derivatives) most pronounced hydroxy-substituted benzoates, especially those OH group position 3 carboxylate group.