Design and optimization of a chemometrics-assisted spectrophotometric method for the simultaneous determination of levodopa and carbidopa in pharmaceutical products

A chemometrics-assisted spectrophotometric method was developed and validated for the simultaneous determination of levodopa and carbidopa in pharmaceutical preparations. Levodopa [3-(3,4-dihydroxyphenyl)-L-alanine] is an aminoacid precursor of the neurotransmitter dopamine, widely used in the treatment of Parkinson's disease, and usually associated with the decarboxilase inhibitor carbidopa [(S)-3-(3,4 dihydroxyphenyl)-2-hydrazino-2-methylpropionic acid]. The multivariate absorbance signals were recorded at a fixed optimum time (4 min) after reaction of the analytes with potassium periodate. The working pH (4.8) and oxidant concentration (1.6 × 10−3 M) were estimated using a two-factor surface response optimization procedure. Calibration and prediction were performed with the aid of the partial least-squares model. The recoveries were satisfactory and statistically comparable to those obtained by applying the reference Pharmacopoeia method of high performance liquid chromatography.