Indirect Spectrophotometric Determination of Methyldopa using AuNPs-Cr(VI)

A simple, sensitive, and rapid spectrophotometric method was suggested for the indirect determination of methyldopa. The method depends on the chemical reaction between citrate-stabilized gold nanoparticles and chromium (III) ions, which form during methyldopa oxidation through potassium dichromate. The process results in nanoparticle aggregation, while the solution transitions from red to blue-grey, and the plasmon band moves from 528 nm to 640 nm. The absorption rate increased linearly within the concentration range of 60-140 ng/ml, while the detection limit reached 27 ng/mL. The proposed method showed excellent accuracy and precision because the mean recovery value reached 100.16%, and the relative standard deviation stayed under 1%. The method produced results that matched the labeled content of methyldopa tablet formulations, which demonstrated its effectiveness for pharmaceutical testing.