Flow analysis-spectrophotometric determination of L-Dopa in pharmaceutical formulations by reaction with p-aminophenol

A new method has been developed for the spectrophotometric determination of L-Dopa in pharmaceutical formulations. The method is based on the reaction between the open-chain quinone of L-Dopa, obtained in NaOH, and the benzoquinoneimine form of p-aminophenol, in the presence of KIO(4). The reaction product is determined at 574 nm by using both alternately procedures, one based on the stopped-flow and another on a flow injection approach. Under the best experimental conditions L-Dopa can be determined with a limit of detection of 52 ng/ml and a relative standard deviation of 0.2% for three replicate measurements of a solution containing 4 microg/ml.