Spectrophotometric and standard addition methods for quantitative determination of dopamine hydrochloride and levodopa in tablets and ampoules

Abstract

A Simple, accurate and sensitive spectrophotometric method for determining dopamine hydrochloride (DO·HCl) and levodopa (LD) in either pure forms or in their commercially available pharmaceutical formularions is reported.
The main idea of the method is based on reacting a solution
of DO.HCl or LD at pH 12; using universal buffer, with
4-aminoantipyrine (4-AAP) to form pink coloured coupling
dye product with λmax = 475 (ε = 1.46x104 l·mol-1·cm-1) or
454 nm (1.05x104 l·mol-1·cm-1) for DO·HCl and LD drugs,
respectively. Before carrying out Beer’s law, different experimental conditions like time, temperature, sequence of
addition and pH are optimized. The molar ratio method revealed
a 1:1 [active ingredient]:[4-AAP] coupling product.
The common excipients used as additives in pharmaceuticals
are examined in our proposed procedure as interfering
materials. The calibration curves were developed by using
standard DO·HCl and LD with percent recovery of 98.62
– 102.9 and 97.40 – 101.5%, respectively. Beer’s law was
obeyed in the concentration range from 37.90 – 170.6 and
49.30 – 221.8 mg/L of DO·HCl and LD, respectively. The
reproducibility and accuracy of the method was checked
by the values of SD = 0.04-0.22 and 0.05-0.15 and RSD
= 0.06-0.16 and 0.02-0.10% for DO·HCl and LD, respectively.
The results compare favourably with those of official and reported methods as indicated by the t- and F-test values, indicating the possibility of applying this spectrophotometric
method in routine measurements.