Related substances.

A simple, precise, accurate, simultaneous and stability-indicating HPLC method developed with an effective resolution of active pharmaceutical ingredients. The present method effectively separates all the related substances of Diphenhydramine hydrochloride and acetaminophen along with impurities. Chromatographic separation has been obtained on Inertsil C18 (250 X 4.6mm, 5µ) column using a gradient elution with a mixture of phosphate buffer pH3.0 and acetonitrile. At 220 nm compounds will be eluted and monitored. Diphenhydramine hydrochloride and acetaminophen were subjected to the stress conditions of acid, base, peroxide, thermal, photolytic, humidity and water degradation. The degradation products were well resolved from main peak and its impurities, proving the stability-indicating ability of the method. The developed method was validated as per International Conference on Harmonization (ICH) guidelines and validation acceptance criteria were met in all cases. The current method has proven good linearity and accuracy over the range of all known impurities from LOQ to 150% of the target concentration. The degree of reproducibility, as results obtained by deliberate changes in the method parameter and variety of condition has proven that the method is robust and rugged.