The purpose of this book is to provide guidance for the development of an analytical method on HPLC for the analysis of active pharmaceutical ingredients of pharmaceutical formulation. Topics included are basic method development and its validation according to ICH guideline. This manual will only cover the use of reverse phase chromatography. HPLC assays are used to demonstrate control of the process, to track and minimize impurities, and to maximize the yield and purity of the isolated product. Characterized working standards are utilized for quantification. In this thesis work has been carried out for the determination of Guaifenesin and Pseudoephedrine hydrochloride in cold and cough preparartios.