IONIC ASSOCIATE OF BENDAZOL WITH METHYL ORANGE AND ITS ANALYTICAL APLICATION

Abstract

It was shown that bendazole (BEN) with methyl orange (MO) forms an ion associate (IA), with the precipitation of which pure compounds were isolated and plasticized membrane potentiometric bendazole-sensitive ion-selective electrodes were created. The possibility of formation of IA is substantiated by the method of computer calculations. Computer calculations of the “MO- + BEN+” systems were performed using the “HyperChem 8.0” program package for various initial combinations of counterion locations («single point» procedure). Geometrical optimization of ions was carried out using the MM+ molecular mechanics method. The standard energy of formation of ions and the associate “BEN+ + MO-” was determined by the semi-empirical PM3 method. The difference in the heat of formation of the ionic associate and the sum of the energies of formation of the cation and anion is 75.4 kJ/mol. This fact substantiates the profitability of the formation of the target compound. On the basis of the obtained IA, plasticized membranes were synthesized and bendazole-sensitive ion-selective electrodes were constructed. The chemical and analytical characteristics of such electrodes are affected by a number of factors, in particular, the properties of plasticizers, the content of the ionic associate in the membrane, etc. The best results were obtained with the use of tricresyl phosphate and dinonyl phthalate. When using other plasticizers, not entirely satisfactory results were obtained. This is most likely related to their dielectric constant and other parameters. At pH 2–5, the best electrodes showed satisfactory functioning. The stability of the potential is 2–3 mV/day and is established in 8–13 seconds. The working life of the developed electrodes is monitored for at least four months. The developed bendazole-sensitive electrodes show reliable results in the presence of a number of substances and ions. show satisfactory selectivity in relation to a number of substances and ions. For the determination of bendazole, a potentiometric determination technique was developed, which was tested in its determination in medicinal forms.