Potentiometric sensor for determination of amprolium in pharmaceutical formulation

Abstract

The interaction of organic cation Amprolium with methyl orange was investigated with the help of thermal studies. The thermolysis of IA Amprolium with methyl orange begins at 20 °C and is characterized by the fact that the molecule of ammonia is released at the first stage at a temperature of 50 °C. In the process of thermolysis no sulfur is released, and we observe a slight exoeffect at 220 °C. Then we observe a small endoeffect at 260 °C. The mass loss at this stage is 34%, which may correspond to the allocation of NH3, SO2, CO and N2, which were identified by qualitative reactions. At the last stage, within the limits of 440-680 °C, combustion of IA occurs, which is accompanied by an exothermic effect at a temperature of 485, 610 °C and endothermic at 520 °C with a significant loss in mass. These slightly soluble associates were used as electrode active substances (EAS) in plasticized polyvinyl chloride (PVC) membranes of ion-selective electrodes (ISE), sensitive to organic cation Amprolium. The influence of the nature of plasticizer on the basic electroanalytical characteristics in the system is investigated. The following organic solvents with corresponding dielectric constant (ε) and Rorschneider polarity (PR) were investigated as membrane plasticizers: diethyl phtalate (8.15; 40), dibutyl phtalate (6.1-6.4; 38), dibutyl sebacate, dioctyl phtalate (5.1; 30), dinonyl phtalate (4.47; 26), tricresyl phosphate (6.7-7; 25). The results of the study of the electroanalytical properties of the sensors developed by the nature of the plasticizer indicate that the best plasticizer for the system is TFC or DNP. For these solvents work of size of the dielectric constant and the Rorschneider polarity are 123.5 and 175, respectively. For plasticizers which appeared less more effective (DBP and DEP) these sizes are 235.6 and 326, accordingly. For membranes with identical content of plasticizer of one homological row (DEP, DBP, DOP, DNF), the Nernstian slope diminishes with growth of dielectric constant of solvent-plasticizer The pH working range of the sensors based on ion associates with methyl orange are 5.5-10.0 respectively. The linearity ranges of the electrode are in the range 6.3×10-5–1×10-1 mol/L, and the function slope is 28-35 mV/decade. The efficiency of the use of sensor for determination of Amprolium in pharmaceuticals was shown.