Peroxidase-based spectrophotometric methods for the determination of ascorbic acid, norepinephrine, epinephrine, dopamine and levodopa

A novel method was developed for the spectrophotometric determinations of ascorbic acid, norepinephrine, epinephrine, dopamine and levodopa. It is based on interference with peroxidase activity, which caused a decrease of the rate of the coupling reaction of p-chlorophenol with 4-aminoantipyrine. The mechanism of interference was studied in a preliminary way, and optimal experimental conditions for the determinations were established. Analysis of commercial pharmaceutical formulations showed excellent correlation with the nominal values given by the manufacturers and with the results of the official methods for the same samples.