The use of tetracyanoethylene as a photometric reagent in analysis of pharmaceutical preparations

Abstract

A possibility of using tetracyanoethylene (TCNE) as a photometric reagent for determination of the dipyrone content in pharmaceuticals is considered. A photometric form was obtained in the aqueous phase in an acetate buffer medium (pH 3.13). The resulting π-complex revealed two absorption bands at (400 and 420) nm with molar absorption coefficients of 1.56 Ч 10⁴ and 1.62 Ч 10⁴, respectively. Due to a high lability of the photometric reagent, the optical density of the complex thus formed must be measured immediately after preparation. The composition and possible mechanism of π-complex formation were determined using the methods of molar ratios and isomolar series: the active substance interacts with the reagent in a molar ratio 1:1. The calculated value of the stability constant of the formed π-complex was 1.42 Ч 10⁶. Proceeding from the obtained data, a spectrophotometric method of dipyrone determination in drugs is developed with a detection limit of 42.63 μg/ml (the error of determination being below 3.0%). The linear dependence of the analytical signal on the concentration of the active substance is observed in the range of 20 – 100 μg/ml. Testing of the spectrophotometric method for dipyrone determination was carried out on tablets and injection solutions manufactured in Russia. There is a good convergence between the results of dipyrone determination by the developed and arbitration methods (pharmacopoeia monograph 2.1.0003.15). The analysis revealed that the content of dipyrone in the dosage form corresponds to the declared. The developed technique is easy to use accessible in equipment and can be recommended for determination of dipyrone in conditions of a conventional analytical laboratory.