Use O-phenylenediamine as an oxidative coupling reagent in the spectrophotometric determination of an antihistamine

A simple and sensitive spectrophotometric method was developed for the determination of an antihistamine, (LD), due to its therapeutic importance in allergic diseases of the nose and eyes in its pure form and in pharmaceutical preparations. The reaction was based on oxidative coupling with O-phenylenediamine in the presence of potassium iodate KIO3 in an acidic solution, resulting in a stable, water-soluble orange solution that gave maximum absorption at 453 nm. After studying the reaction conditions, including the concentration and volume of the reagent, the type and concentration of the acid used in the reaction medium, in addition to other factors such as reaction time and temperature, it was found that the method obeyed the Beer-Lambert law with a range of concentrations of the drug compound (LD) that ranged between 1-30 μg/ml, and the molar absorbance value was 11065.232 L/mol.cm while the Sandell's sensitivity was 0.03460 µg/cm2. As for the limits of detection, LOD and LOQ, they were 0.114 µg/mL and 0.346 µg/mL, respectively. The results indicated that there were no interferences of excipients in the proposed LD estimation process. The method has been successfully applied to estimate the drug compound LD in pharmaceutical preparations.