RESULTS AND DISCUSSION Method development and optimization of stability indicating assay method The method was optimized to separate major degradation products formed under varies stress conditions. I (pKa = 4.4) is acetic compound, whereas FM (pKa = 7.1) is basic compound. The main target of the chromatographic method is to get the separation for closely eluting degradation products. The degradation samples were run using different stationary phases like C18, C8, Cyano, and mobile phases containing buffers like phosphate, sulfate, and acetate with different pH (2-7) and using organic modifiers like acetonitrile and methanol in the mobile phase. But, the separation was satisfactory in the adopted chromatographic conditions only [Table 1 and Figure 2] the optimized conditions are, the mobile phase A was a mixture of pH 5.5 buffer and methanol in the ratio of 85:15(v/v), respectively, and the mobile phase B contains a mixture of pH 5.5 buffer and methanol in the ratio of 75:25 (v/v), respectively. Table 1 Results from system suitability test Figure 2 A typical HPLC chromatogram of Famotidine and Ibuprofen from tables. Specificity �C forced degradation studies Forced degradation studies were performed on IB and FM to prove the stability-indicating property of the method. The stress conditions employed for degradation study of FM and IB include light exposure, heat (100��C), acid hydrolysis (1 N HCl), base hydrolysis (1 N NaOH), water hydrolysis, and oxidation (3% H2O2). For light studies, the monitoring period was 10 days, whereas for heat, acid, base, and water hydrolysis, it was 24 h. Oxidation was carried out for 2 h. Peak purity of the principal peak in the chromatogram of stressed samples of IB and FM tablets was checked using photo diode array detector. Degradation was not observed in IB and FM stressed samples that were subjected to light and water hydrolysis. However, the degradation was observed under heat, oxidative conditions, base hydrolysis, and acid hydrolysis. The peak purity test results derived from PDA (Photo Diode Array detector) confirmed that the IB and FM peaks were pure and homogeneous in all the analyzed stress [Table 2]. This indicates that the method is specific and stability indicating. Table 2 Summary of results from forced degradation experiments Validation Method validation was performed as per ICH guidance for simultaneous determination of IB and FM in the formulations. The following validation characteristics were addressed, linearity, detection limit, quantification limit, precision, accuracy, robustness, ruggedness, and specificity.[18�C20] Precision The precision of an analytical method gives information on the random error. It expresses of agreement between a series of measurements obtained from multiple sampling of the same homogeneous sample under prescribed conditions. The percentage RSD values for the precision study was 0.