Spectrophotometric Determination of Phenylephrine Macromolecule by Coupling with Diazotized 4-Bromo Aniline

The present study outlines a meticulously devised and accurate spectrophotometric method for the determination of phenylephrine hydrochloride (PHEPH) in both its pure drug form and drop formulation. The methodology hinges upon a diazo-coupling reaction, whereby PHEPH undergoes coupling with diazotized 4-bromoaniline under alkaline conditions. The resulting yellowish-orange azo-dye demonstrates a remarkable sensitivity, quantified by the molar absorptivity value of 4.684 × 10³ L mol⁻¹ cm⁻¹. The pinnacle of absorption occurs at 459 nm, and the linearity of the method is impeccably upheld within the concentration range of 3–48 µg 10 mL⁻¹ of PHEPH, as dictated by Beer's law. An aspect of paramount significance is the enduring stability of the product's coloration, evincing minimal alteration in absorbance over duration of up to 60 min. Notably, the recovery percentage stands at an impressive 100.1376%, testifying to the method's accuracy, while the relative standard deviation (RSD%) of a mere 0.310178% underscores its precision. The applicability of this method extends seamlessly to the estimation of PHEPH within nasal drop formulations, yielding results of commendable reliability and consistency.