Потенціометричне кількісне визначення хондроїтин натрію сульфату з використанням іонселективних електродів

Chondroitin sodium sulfate is an anionic polysaccharide widely used in pharmaceutical practice as an active ingredient of mono- and multicomponent medicinal products, and its quantitative determination is an essential stage of the quality control. It has been found that the application of potentiometric titration with ion-selective electrodes can increase the accuracy and objectivity of the quantitative analysis, which is of great importance for ensuring the quality and safety of medicines. The aim of the study was to develop and validate a potentiometric method for the quantitative determination of chondroitin sodium sulfate in the substance and in a combined medicinal product in the form of the sachet powder. The study objects were chondroitin sodium sulfate substance and a combined medicinal product containing chondroitin sodium sulfate in combination with D-glucosamine sodium sulfate, methylsulfonylmethane, sodium hyaluronate, ascorbic and citric acids, and sorbitol. The conditions of the potentiometric titration with 0.001 M solution of cetylpyridinium chloride were studied using an ion-selective electrode based on cetylpyridinium ionic associates with some lipophilic anions. The titrant was standardized using sodium dodecyl sulfate as a primary standard, as well as the substance itself. The equivalence point was determined from the titration curve and its mathematically processed forms (differential curve, first derivative, and Gran functions). It has been found that the plasticized membrane ion-selective electrodes based on cetylpyridinium associates with dodecyl sulfate and tetraphenylborate anions are characterized by a stable near-Nernstian response in the operating range of cetylpyridinium concentrations of 10-3-10-6 mol L-1. The analytical characteristics of the electrodes remained stable for at least 30 consecutive titrations. The selectivity of the reaction between chondroitin sodium sulfate and cetylpyridinium chloride was found, ensuring a clear determination of the equivalence point even in the presence of other mixture components. The influence of pH on the titration results was evaluated; it was shown that in the pH range of 4-8 the shape of titration curves and potential values remained constant, confirming the robustness of the method. The accuracy, precision, linearity (within 80–120% of the nominal content of the analyte), and the reproducibility of the method were characterized. It has been experimentally demonstrated that the potentiometric method proposed is accurate, selective, and reproducible for the quantitative determination of chondroitin sodium sulfate both in pure form and in combined medicinal products. The results obtained confirm the analytical suitability of the method developed and the prospects of its implementation in the pharmaceutical analysis practice for the quality control of substances and combined medicinal products of small-scale and industrial production.