Investigating the physicochemical properties of phenazopyridine hydrochloride using high-performance liquid chromatography and uv-visible spectrophotometry

The purpose of this study is to develop high-performance liquid chromatography (HPLC) and ultraviolet-visible (UV-Vis) spectrophotometry methods for the determination of pKa, log P, and log D values of phenazopyridine hydrochloride (PHCl). For the HPLC analysis, the pH of the mobile phase was plotted against the capacity factor, and the pKa value was obtained from a sigmoidal relationship. Meanwhile, for the UV-Vis spectrophotometric study, the absorbance of PHCl was plotted against pH at 332 nm to obtain the pKa value. The log P and log D (at pH 2.0) values were then calculated based on the concentration of PHCl in the octanol/water phase. Using the HPLC method, the pKa value was established as 5.05 (± 0.15). Meanwhile, the spectroscopic technique afforded pKa values of 5.20 (± 0.22) and 5.17 (± 0.17) via a classical sigmoidal curve and the Albert and Serjeant method. The log D (at pH 2.0) and log P values of PHCl were 1.61 (± 0.16) and 2.62 (± 0.11), respectively. The obtained results are in good agreement with each other. The pKa, log P, and log D values of PHCl can be determined by HPLC and UV-Vis spectrophotometry with reproducible results.