Simultaneous kinetic-spectrofluorometric determination of levodopa and carbidopa using partial least-squares regression.

A simple and sensitive methodology for the simultaneous determination of levodopa and carbidopa in pharmaceutical samples is described. The method combines the advantages of fluorescence with partial least-squares (PLS) analysis, and requires no previous separation steps. The developed method is based on the oxidation of levodopa and carbidopa by cerium(IV) in a sulfuric acid medium and monitoring the fluorescence of the formed Ce(III) at lambda(exc) = 255 nm and lambda(em) = 355 nm. PLS uses differences in the reaction rates as a discriminatory parameter, and regresses the data of fluorescence vs. time onto the concentrations of the standards. Eight validation samples and seven commercial tablets were studied, using a nine-sample aqueous calibration set. The analyte recoveries from pharmaceuticals ranged from 98 to 101% for levodopa and from 100 to 108% for carbidopa. The results obtained by the developed method were statistically comparable to those obtained with high-performance liquid chromatography.