A simple and efficient method for simultaneous quantification of levodopa and carbidopa based on controlled oxidation process

Abstract

Levodopa (L-dopa) and carbidopa (C-dopa) are used for the treatment of the Parkinson’s disease. In the present work, an experimental and theoretical investigation about oxidation process of these drugs was able to provide the optimal conditions of an efficient analytical method for simultaneous quantification of L-dopa and C-dopa in pharmaceutical preparations. The theoretical results, based on density functional theory (DFT), have shown good agreement with the experimental UV–Vis findings, thus providing new insights into the oxidation mechanisms of these drugs. The analytical procedure is based on the controlled oxidation of these drugs, with further quantification using UV absorption spectrophotometry. The present method has been validated, showing good linearity over the ranges of 3.88–42.68 µg mL−1 for L-dopa and 2.2–11.00 µg mL−1 for C-dopa. Precision measures were satisfactory with the relative standard deviation values lower than 2.31% in all analytical tests; accuracy was verified by recovery studies and also by method comparison, showing excellent results. Mean of recoveries was within the acceptable limits of 96.14–101.84% for both drugs. The proposed method showed to be selective at pH 13.5 allowing the determination of both drugs without interference spectral to each other or from excipients of the Parkidopa®, pharmaceutical preparation studied in this work. The present method represents an interesting, rapid, inexpensive and environmentally friendly alternative method for the quality control analysis of this pharmaceutical preparation.