Spectroscopic Characterization of the Oligomeric Product from Oxidative Coupling of Amoxicillin with the Macromolecular Dye Crystal Violet

ABSTRACT A colorimetric method was developed for the spectrophotometric determination of amoxicillin (AMOX) based on an oxidative coupling reaction. In this method, amoxicillin was oxidized using potassium permanganate (KMnO 4 ) as an oxidizing agent, followed by a coupling reaction with crystal violet (CV) dye in a basic medium. This reaction produced a reddish‐brown product exhibiting maximum absorbance at 590 nm, using water as a solvent. Optimal conditions for complex formation—oxidation time, coupling time, temperature, oxidant concentration, reagent concentration, and base concentration—were thoroughly investigated. The method showed linearity in the concentration range of 10–40 µg/mL, with a correlation coefficient (R 2 ) of 0.998. The molar absorptivity was found to be 11 388 L/mol·cm. Sandell's sensitivity was 0.032 µg/cm 2 , while the limits of detection (LOD) and quantification (LOQ) were 0.373 µg/mL and 1.132 µg/mL, respectively. Recovery values ranged from 96.217% to 103.397%, with relative standard deviation (between 0.077% and 3.978%. These results indicate that the proposed method is accurate, sensitive, and successfully applicable for the determination of amoxicillin in its pharmaceutical formulations.