STABILITY-INDICATING CHROMATOGRAPHIC METHOD FOR THE DETERMINATION OF BENZONATATE, DIPHENHYDRAMINE, GUAIFENESIN, AND PHENYLEPHRINE

A high-performance liquid chromatographic method has been developed for the simultaneous analysis of benzonatate (BNZ), diphenhydramine hydrochloride (DPH), guaifenesin (GFN), and phenylephrine hydrochloride (PEP). The separation was achieved using a Thermo C18 reversed-phase column (250 mm × 4.6 mm ID, particle size 5 µ). Dual mode gradient elution was used for the separation and UV detection was carried out at 222 nm. The method was specific and stability indicating as chromatographic conditions provided adequate separation of degradation products. The method showed good linearity in the range of 5–400, 1–120, 3–300, and 2–100 µg/mL for BNZ, DPH, GFN, and PEP, respectively. All the square of the correlation coefficients are 0.999. The degradation products were isolated and identified by NMR, IR, and mass spectroscopy. The proposed method proved to be accurate, precise, selective, and robust. The applicability of the method was evaluated in commercial dosage form analysis as well as in stability studies.