Redox-Based Colorimetric Sensor for the Selective Determination of Ascorbic Acid in Fixed-Dose Combination Tablets

Abstract

Background Ascorbic acid (ASC; vitamin C) is a weak chromophoric substance, so its presence cannot be determined directly by spectrophotometry. Objective This work aims to develop and validate a simple and ecofriendly analytical method for the determination of ASC concentration based on the reaction of ASC with the metal complex ferric salicylate. Method The visible absorbance of ferric salicylate was found to be inversely proportional to the concentration of ASC. The possible mechanism of the reaction between ASC and ferric salicylate was investigated: ferric salicylate was found to be reduced by ASC under the applied experimental conditions. Different parameters that may affect the reaction were also investigated: ferric salicylate concentration, pH, ionic strength, and the time of reaction. The optimum concentration of ferric salicylate was found to be 1000 µM and the optimum pH was 5.5. The developed method was validated according to ICH guidelines. Results The linearity range of the developed method was 5–70 µg/mL and the correlation coefficient was 0.9994. The limits of detection and quantitation were 0.38 µg/mL and 1.16 µg/mL, respectively. The method was successfully applied to the determination of ASC concentration in commercial Ruta-C60® tablets. The mean % recovery ± standard deviation was found to be 101.10 ± 0.70. The results were statistically compared to those obtained by a reported high performance liquid chromatographic method. Good agreement was observed. Conclusion The developed method is simple, fast, cost-effective, and suitable for routine pharmaceutical analysis of ASC. Highlights The developed method is more sensitive than the other spectrophotometric methods reported for determination of ASC.