Kinetic-Spectrophotometric Determination of L-Dopa, Methyldopa, Dopamine and Adrenaline

Abstract

A simple, sensitive and reliable method is proposed for the determination of trace quantities of L-dopa, methyldopa, dopamine and adrenaline. The method is based on the inhibition effect of these catecholamines on the reaction of nitrite with neutral red in acidic media. The reaction is monitored spectrophotometrically by measuring the decrease in the absorbance of neutral red solution at 530
nm with a fixed time method of 3 min. The calibration graphs were
linear in the ranges of 3.05 x 10^–6-1.62 x 10^–5M for L-dopa,
1.8 x 10^–6-1.33 xl0^–5 M for methyldopa, 2.61 x 10^–6-2.67 x 10^–5
M for dopamine and 1.59 x 10^–6-3.27 X 10^–6 M for adrenaline. This
method was applied for the determination of the catecholarnines in
pharmaceutical formulations with satisfactory results.