The scientific way to develop a simple and robust analytical HPLC method for the critical separationsis QbD approach. Quality-by-design (QbD) is a systematic approach to product or process development, which begins with predefined objectives, and uses science and risk management approaches to gainproduct and process understanding and ultimately process control. The concept of QbD canbe extended to analytical methods. A simple Analytical method was developed and used to identify and quantify simultaneously the two active pharmaceutical ingredients Resperidone and Benzoic acid. In the present work, three independent factors were used such as flow rate (A), wavelength (B) and pH of buffer (C). Totally 27 experimental runs were suggested by the software for analyzing the interaction of each level on formulation characters and the peak area (R1), tailing factor (5%) (R2) and number of theoretical plate USP (NTP) (R3) were considered as response factors (dependent factors). The significance of independent factors was determined using Fisher’s statistical test for Analysis of the Variance (ANOVA) model that was estimated. Waters Xterra C-18 column (150 mm × 4.6 mm, 5 μm pore size), column was the most suitable one since it produced symmetrical peaks with better resolution. The UV detector response of RIS and BA was studied and the best wavelength was found to be 275 nm showing highest sensitivity of both compounds. The method was validated for specificity, reproducibility, accuracy, linearity, robustness and solution stability and can be used for the assessment of quality of drug product in development and stability samples of the marketed oral solution. The target degradation for the stability indicating ability of the assay method was tried in the present study and there was no any interfering peaks found due to degradation products.
