Spectrophotometric Determination of Five Commercial Drugs in Pure Form and Pharmaceutical Formulations by Ion-Pair Complexation with Alizarin Red S

Abstract

Simple, accurate, selective and rapid spectrophotometric methods have been developed for the
determination of itopride, midodrine, diclofenac, mesalamine and sumatriptan in their pure as well as
in pharmaceutical dosage forms. The method was based on ion-pair complex formation between the
drugs and anionic dye, alizarin red S in an acidic medium (pH 2.0-4.0). The complexes formed were
quantitatively extracted into chloroform and measured at 284, 287, 279, 285 and 280 nm wavelength
for itopride, midodrine, diclofenac, mesalamine and sumatriptan respectively. Beer’s law was obeyed
in the concentration range of 3.5-35 µg mL-1 for itopride and diclofenac, 2.5-180 µg mL-1 for
midodrine, 3.0-80 µg mL-1 for mesalamine and 4.0-200 µg mL-1 for sumatriptan. The stoichiometry of
the complexes formed between the drugs and the dye was 1:1 as determined by Job’s method of
continuous variation. The association constant (KIP) of the ion-pair complexes formed was evaluated
using Benesi-Hildebrand equation. Limit of detection, limit of quantification and Sandell’s sensitivity
of the methods were also estimated. The proposed methods were successfully employed for the
determination of these drugs in their pharmaceutical dosage forms.