Aim. To develop a new kinetic spectrophotometric enzymatic method suitable for the quantitative determination of dequalinium chloride in lozenges.Materials and methods. An enzymatic kinetic spectrophotometric method for the quantitative determination of dequalinium chloride in lozenges  has been proposed. It is based on the ability of dequalinium chloride to inhibit the enzymatic hydrolysis reaction of acetylcholine by cholinesterase in the presence of the acetylcholine (AСh) excess and H2O2. The degree of inhibition was determined by the kinetic method using two conjugated reactions: ACh perhydrolysis (interaction with an excess of hydrogen peroxide) followed by oxidation with the peroxyacid formed. Peracetic acid formed in situ by the reaction between unreacted ACh and H2O2 interacts with p-phenetidine forming a product, which absorbs at λmax = 354 nm, in the phosphate buffer solution with pH 8.3 at room temperature.Results and discussion. The linear dependence of the calibration graph for the quantitative determination of dequalinium chloride was in the concentration range of 0.2 – 0.8 μg mL–1 (r = 0.999). LOD and LOQ were 0.01 × 10–6 and 0.03 × 10–6 mol L–1, respectively. For the quantitative determination of dequalinium chloride in lozenges, RSD ≤ 2.65 % (accuracy, δ = -1.10…+1.78 %).Conclusions. A new enzymatic kinetic spectrophotometric method has been developed, and its applicability to the quantitative determination of dequalinium chloride in lozenges has been shown. It does not require a complicated treatment of the analyte and a tedious extraction procedure. The method proposed is sensitive enough to determine a small amount of the active pharmaceutical ingredient. These advantages encourage the application of the method proposed in routine quality control of the drugs studied in analytical laboratories.

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Aim. To develop a principally new method, which would allow achieving the necessary accuracy and reproducibility of the analysis results, for determining the activity of the blood cholinesterase; to create safe working conditions when performing the analysis. Results and discussion. The kinetic method proposed for determining the activity of cholinesterase consists in photometric measurement of the rate of the enzymatic hydrolysis of the acetylcholine substrate (by its residue) in the phosphate buffer using p-phenetidine as an indicator. The rate of the enzymatic hydrolysis of acetylcholine was determined by the tangent of the inclination angle of the linear part of the kinetic curve in the А–t coordinates at a wavelength of 358 nm. The linear dependence of the conditional reaction rate (tgα) on the enzyme concentration was observed in the concentration range of 0.12 – 0.36 mg/mL. Metrological characteristics of the method developed were: RSD = 2.0 % (n = 5; P = 0.95), correctness 0.4 %. These values indicate that the method for determining the activity of blood cholinesterase is sensitive, reliable and reproducible. Experimental part. The experiments on determining the rate of the enzymatic hydrolysis were repeated three times with a specific concentration of the enzyme. Using the data obtained the kinetic curves were constructed in the А–t coordinates; on their basis the tangents of the angles of inclination in min-1 were calculated. The calibration graph was constructed using the average values of the tangents of the angles of inclination, which corresponded to a certain concentration of the solution of the working standard sample of the enzyme. The equation of the calibration dependence of tgα-enzyme concentration was calculated by the method of least squares and found to be tgα (min-1) = –0.17с + 9.13 (r = 0.999). Conclusions. As a result of the studies conducted, a new method for determining the activity of the cholinesterase enzyme has been developed. The method is characterized by a high sensitivity, reliability and reproducibility and provides safe working conditions when performing the analysis.

Objetivos: Se ha desarrollado un nuevo método fotométrico cinético sensible para la determinación de la presencia del cloruro de benzalconio. Material y métodos: El método se basa en la capacidad de inhibir la hidrolisis de acetilcolina en presencia de colinesterasa. La velocidad de reacción se estima mediante el residuo no hidrolizado de acetilcolina, que está determinado por la cantidad de ácido peracetico formado durante la interacción de la acetilcolina con el exceso de peróxido de hidrogeno. La reacción indicativa es la interacción de -etoxianilina con ácido peracetico, que da como resultado la formación de 4,4’-azoxifenetol con λmax = 358 nm ((log10 =4.2). Resultados: Las condiciones óptimas seleccionadas para llevar a cabo el experimento. El experimento se llevó a cabo en el rango de concentraciones (1.4 to 8.4·10-6 mol L-1 de cloruro de benzalconio. el coeficiente de correlación fue 0.999. Los límites de la definición de análisis (20% del grado de inhibición) fueron 1.9·10-6 mol L-1. Conclusiones: El método propuesto se aplicó con éxito en el análisis de gotas oculares у permitió confirmar la precisión у fiabilidad de los resultados.