Potentiometric determination of threonine in acid solutions by used MF-4SC membranes with sulfo-containing dopants
Amino acids are components of pharmaceuticals, products for children and sports nutrition, and also they use as feed additives. The electrochemical methods, in particular dialysis and electrodialysis, are being developed for the separation and purification of amino acids. The necessity to control of processes efficiency and the quality of products in the production of amino acids necessitates the development of methods for their rapid determination, taking into account the variable medium pH. The aim of this work was to reduce the influence of hydroxonium ions on the determination of threonine cations and zwitterions in aqueous solutions at pH-4 to 1.0 10-1 М. In the pH range of the investigated solutions (1.73-4.25), threonine is present in the form of singly charged cations (Thr+) and zwitterions (Thr±). The perfluorosulfonic membranes (MF-4SC) and the hybrid materials based on them with nanoparticles of hydrated zirconia and silica, surface modified by the -(CH2)3-SO3H and -SO3H sulfo containing fragments, were used as materials for DP-sensors. The samples of membranes were provided by the Laboratory of Ionics of Functional Materials of the Kurnakov Institute of General and Inorganic Chemistry RAS (the head of laboratory is Yaroslavtsev A.B., Dr.Sci. (Chemistry), prof., corresponding member of the RAS;a synthesis of materials is carried out by Safronova E.Yu., senior scientific researcher, Ph.D. (Chemistry)). The influence of the concentration and proton-donor properties of dopants introduced into the membranes on the characteristics of cross-sensitive DP-sensors in threonine solutions at pH2)3-SO3H groups. Using these membranes provided a reduction of the relative error determination of threonine cations and zwitterions in 2.5-4 times compared with the initial sample in the concentration range of analyte from 1.010-4 to 1.010"1 M (pH 1.73-4.25).