Factors DOE I DOE II DOE III DOE IV pH -1 = 3 ,0 = 4 ,+1 = 5 -1 = 4 ,0 = 5 ,+1 = 6 -1 = 3.9 ,0 = 4 ,+1 = 4.1 -1 = 3.9 ,0 = 4 ,+1 = 4.1 Flow rate -1 = 0.8 ,0 = 1 ,+1 = 1.2 -1 = 1 ,0 = 1.2 ,+1 = 1.4 -1 = 1.2 ,0 = 1.4 ,+1 = 1.6 -1 = 1.1 ,0 = 1.2 ,+1 = 1.3 Acetonitrile -1 = 40 ,0 = 50 ,+1 = 60 -1 = 55 ,0 = 60 ,+1 = 65 -1 = 62.5 ,0 = 65 ,+1 = 67.5 -1 = 60.5 ,0 = 62.5 ,+1 = 64.5 Wavelength -1 = 220 ,0 = 230 ,+1 = 240 -1 = 210 ,0 = 220 ,+1 = 230 -1 = 229 ,0 = 230 ,+1 = 231 -1 = 229 ,0 = 230 ,+1 = 231

Table 2: Experimental design (DOE I, II, III and IV) to develop and optimize the chromatographic conditions for nifedipine and atenolol mixture.