A Novel Spectrophotometric Approach for the Determination of Vitamin C Using Thiosemicarbazone and Its Application to Pharmaceutical Preparations

A new spectrophotometric method has been developed for the determination of Vitamin C in aqueous solutions. The method is based on the oxidative coupling reaction of Vitamin C with a Thiosemicarbazone reagent in an acidic medium and in the presence of potassium periodate. This reaction yields a stable, water-soluble, dark orange-colored complex exhibiting maximum absorbance at a wavelength of 490 nm. The method obeys Beer’s law within a concentration range of (3 to 120 µg/mL), with a molar absorptivity of (4174.24 L·mol⁻¹·cm⁻¹) and a Sandell’s sensitivity index of (0.0421 µg/cm²); the limit of detection (LOD) is (0.0753 µg/mL), and the limit of quantitation (LOQ) is (0.251 µg/mL). The method has been successfully applied to the determination of Vitamin C in pharmaceutical tablets.