Figure 7: Typical HPLC chromatograms obtained from 20 μl injections of Amlodipine Besylate Amlodipine impurity A, B, Atorvastatin Calcium, Atorvastatin impurity A and C under chromatographic conditions of a mobile phase consisted of acetonitrile: phosphate buffer was pumped on Thermo BDS HYPERSIL Cyano (5um, 250 X 4.6 mm) column at a flow rate 1.2 ml/ min and detected at 240 nm at constant temperature 40°C. (Ascending order) 1-acetonitrile 35 %: phosphate buffer 65% PH=6.5 2-acetonitrile 35 %: phosphate buffer 65% PH=4.5 3-acetonitrile 30 %: phosphate buffer 70% PH=4.5 4-acetonitrile 25 %: phosphate buffer 75% PH=4.5 5-acetonitrile 35 %: phosphate buffer 65% PH=2.5 6-acetonitrile 30 %: phosphate buffer 65% PH=2.5