SUMMARY
A simple and express method for the quantitative determination of zopiclone in model solutions of the substance and in “Zopiclone” tablets, 7.5 mg, by the kinetic-spectrophotometric method according to 3,3’,5,5’-tetramethylbenzidine oxidation has been developed. It is based on the system of two coupled reaction: 4-methyl-1-piperazineperoxycarboxylic acid generated in zopiclone perhydrolysis reacts with the excess of hydrogen peroxide in the weak alkaline medium with formation of coloured 3,3’,5,5’-tetramethyldiphenylquinone diimine (?max = 420 nm, ?? = 8.4). The reaction is performed spectrophotometrically by measuring the rate of change of the absorbance at 420 nm. The method was used for constructing the calibration graph. The initial rate of the reaction was obtained from the linear site of the slope of the initial tangent to the absorbance-time curve. In the pH range of 8.2-8.5 the rate of the coloured product formation becomes maximum. The calibration graph for zopiclone has a linear dependence in the range of 6-36 mg/l with the limit of detection (LOD) and quantitation (LOQ) of 1.81 and 6.04 mg/l, respectively. For five determinations of 18, 24 and 30 mg/l of zopiclone RSD is 1.81, 1.46 and 1.69%, respectively. The analytical performance of the method was validated statistically with respect to LOD, LOQ, accuracy, precision and linearity for zopiclone estimation in a pure substance and the results were satisfactory. “Zopiclone” tablets compared to the reference method contain 99.83±1.19% of C17H17ClN6O3 (RSD = 0.96% , d = -0.17%). The assay of zopiclone in the presence of its hydrolysis products without preliminary separation is an important advantage of the method.