A New Spectrophotometric Method for Determination of Phenylpropanolamine HCl in its Pharmaceutical Formulations via Reaction with 2,3,5,6-tetrachloro-1,4-benzoquinone.

A selective and simple spectrophotometric method has been developed for the determination of phenylpropanolamine HCl (PPA) in its dosage forms. The method was based on the formation of a colored N-vinyl chlorobenzoquinone derivative of PPA through its reaction with 2,3,5,6-tetrachloro-1,4-benzoquinone in presence of acetaldehyde. The colored product exhibits maximum absorbance at 650 nm. Different experimental parameters affecting formation and stability of the product were carefully studied and optimized. The stoichiometry of the reaction was determined, and the reaction pathway was postulated. The absorbance concentration plot was rectilinear over the range of 5-100 μg/mL with Limit of Detection (LOD) and Limit of Quantitation (LOQ) of 0.244 μg/mL and 0.74 μg/mL respectively. The analytical performance of the method was fully validated, and the results were satisfactory. The proposed method was successfully applied to the determination of PPA in its commercial dosage forms including tablets, capsules and syrups with good recoveries. Statistical comparison of the results with those of the comparison method showed good agreement and proved that there was no significant difference in the accuracy and precision between the reference and the proposed methods. The mechanism of the reaction pathway was postulated.