Perfluorinated sulfonated cation-exchange membranes MF-4SC containing 0.5-3.0% of carbon nanotubes (CNTs) have been synthesized. A correlation between the water uptake and transport properties of the membranes in the K +-form and the sensitivity of DP-sensors (with the analytical signal in the form of a Donnan potential) to the analyte and interfering ions in solutions of hydrophobic amino acids (alanine, valine, and phenylalanine) has been found. Hybrid membrane samples that provide the highest sensitivity of DP-sensors to amino acid cations and zwitterions and the lowest sensitivity to hydroxonium ions at pH < 7 in a concentration range of 1.0 × 10-4-1.0 × 10-1 M have been selected. Membrane modification has led to a decrease in the relative error and the relative standard deviation in the determination of amino acid ions by a factor of 3 and 1.5, respectively.

Composite membrane materials based on Nafion-117 gradient modified by poly(3,4-ethylenedioxythiophene) (PEDOT) are prepared by in situ oxidative polymerization. 0.002 M and 0.01 M solutions of the monomer are used for the synthesis of PEDOT, while the concentration of the oxidant is varied. The equilibrium (water uptake, ion exchange capacity) and transport properties (conductivity, diffusion permeability, coefficient of diffusion) of membranes in the H +-and K +-forms are investigated. The influence of the modification of membranes on the characteristics of cross-sensitive Donnan potential (DP) sensors in the aqueous solutions containing sulfacetamide and an alkali in a wide range of values of pH (5.8-11.2) is studied. The array of cross-sensitive DP-sensors based on membranes with different compositions is used to determine the active substance in "Sul'fatsil natriya" pharmaceuticals from various manufacturers. The relative error of determination is 0.5-3%.

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