Application of the enzymatic method for the quantitative determination of dequalinium chloride in lozenges

Abstract

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.