Sequential Injection Kinetic Method for the Assay of Aspirin in Drug Formulations

Original Paper

Abstract

For the first time the sequential injection analysis technique was fully utilized for quantitative kinetic determination of Aspirin and comprehensive reaction rate measurement using permanganate as an oxidant in sulphuric acid media. The absorbance was monitored by the color decrease of permanganate absorbed at the wavelength 525 nm. The reaction orders with respect to Aspirin, permanganate and hydrogen ions were found to be positive one (+1), positive one (+1), and inverse one (-1) respectively. The Reaction mechanism was postulated and a fixed time kinetic method for quantitative analysis of Aspirin was adopted. A full kinetic study was executed resulted in postulating the mechanism of oxidation of Aspirin by permanganate for the validation of a newly adopted kinetic method for quantitative determination of the drug in pharmaceutical preparations. The fixed time kinetic method was applied and the following calibration equation A = -0.09980 + 0.00617 C with r = 0.999 was obtained at a the fixed time exactly 90 s with a flow rate of 25 μl/s. The linearity of the method was found to be ranged between 5 to 400 ppm for the analyte when injecting 30 μl of it and keeping constant concentrations and volumes of 30 μl 2.29 x10^-3 mol l^-1 potassium permanganate, 30 μl 0.05 mol l^-1 sulphuric acid and 20 μl as spacer solution (water). The above calibration equation was employed for quantitative determination of Aspirin in drug formulations in different proprietary tablets. The results obtained proved accurate and precise for the assay of Aspirin in drug formulations without suffering interferences from other active ingredients and any of excipients usually added in tablet formulations.