DP-sensors based on MF-4SC membrane and silica with hydrophobic surface for determination of phenylalanine,valine, and methionine cations

The influence of modification of MF-4SC membranes with silica (or surface-hydrophobized silica) nanoparticles on their ionic conductivity and diffusion permeability as well as the response stability and sensitivity of the membrane-based DP-sensors for cations of amino acids containing hydrophobic fragment has been studied. The membranes modified with surface-hydrophobized silica exhibited the 2–5 times reduced relative error of determination of the hydrophobic amino acids as compared to the initial membranes.     

Ionic Composition of the MK-40 Cation-Exchange Membrane in Amino Acid Solutions: A Conductimetric Study

The ionic composition of a cation-exchange membrane in solutions of amino acids of three types is studied by measuring its conductivity. The concentration constants of equilibrium of the protonation of zwitterions of these acids in the membrane are estimated. The membrane's ionic composition substantially depends on the type of amino acid.     

Limiting current densities in electromembrane systems with carboxyl-containing polyamidoimide membranes

Voltammetric characteristics of electromembrane systems with carboxyl-containing polyamidoimide membranes in 0.01 M solutions of sodium and hydrogen chlorides are studied using a rotating membrane disc. The limiting current density increases with the decrease in the exchange capacity and an increase in the generation temperature and imidization degree of membranes, due to variations in their structures. The difference in the structure of membranes with various exchange capacities is proved by the standard porosimetry method. The distinguishing feature of the limiting state in the HC1 solutions is that the generation of the hydrogen and hydroxyl ions in the near-surface layer occurs long before its concentration exhaustion.     

Potentiometric Cross-Sensitive Sensors Based on Perfluorinated Membranes Treated at Different Relative Humidity for Codetermination of Cations and Anions in Alkaline Solutions of Amino Acids

The results of studying characteristics of potentiometric DP-sensors (sensors with the Donnan potential as their analytical signal) are presented for alkaline solutions of a sulfur-containing amino acid with perfluorosulfonic cation exchange membranes subjected to thermal treatment and mechanical deformation at different relative humidity. Correlation between the distribution of sensitivity of DP-sensors towards cations and anions and diffusion permeability of membranes was found. A multisensor system including two DP-sensors based on membranes with optimized properties and a glass electrode for codetermination of potassium cations and amino acid anions and zwitterions in solutions at pH >7 are developed.     

Determination of sulfur-containing anions in alkaline solutions using arrays of DP-sensors based on hybrid perfluorinated membranes with proton-donor dopants

The influence of proton-donor properties and concentration of dopant nanoparticles introduced into Nafion and MF-4SС perfluorosulfonic cation-exchange membranes on the characteristics of cross-sensitive DP-sensors (sensors whose analytical signal is the Donnan potential) in alkaline solutions of sulfur-containing organic compounds were studied. The dopants were acid salts of heteropoly acids (HPAs) and hydrated silica SiO₂ and zirconia ZrO₂ surface-modified with sulfur-containing groups and an acid HPA salt. A correlation was revealed between the DP-sensor sensitivity to anions (and zwitter-ions) in alkaline solutions, size and proton-donor ability of the added particles, and diffusion permeability of hybrid membranes. Optimum compositions of membranes for arrays of cross-sensitive DP-sensors ensuring the simultaneous determination of cations and anions (and zwitter-ions) in the test solutions with an error of less than 18% were selected.     

Conductivity of systems comprising anion-exchange membranes MA-41 and alkaline glycine solutions

The concentration dependences of the conductivity of 0.001 M NaOH + glycine solutions and the MA-41 anion-exchange membrane are studied. At glycine concentrations c = 0–0.01 M, the solution and membrane conductivities are defined by the glycine and hydroxyl equilibrium concentrations. The charge transport in the solutions proceeds via both hydrodynamic and prototropic mechanisms. At c = 0.01–0.1 M, the contribution from glycine ions carrying the charge via the prototropic mechanism increases. The conductivity of the membrane is determined by the glycine anion deprotonation in it.     

Transfer of Amino Acids through a Membrane/Solution Interface in the Presence of Heterogeneous Chemical Protonation Reaction

A physicochemical model for the transfer of amino acids through the interface between a cation-exchange membrane and an amino acid aqueous solution is proposed. The model allows for a heterogeneous reaction of protonation of the amino acid zwitterion. The model calculations are compared with experimentally determined migration transport numbers for glycine cations in an electromembrane system with an MK-40 membrane. The comparison shows that, owing to the protonation reaction, the glycine flux can increase by ca. 30%.