1 Stationary phase Phenomenex C18 analytical column, (250 mm×4.6 mm, 5 μm) 2 Mobile phase Solvent A: Ammonia solution adjusted the pH to 4.5 with ortho phosphoric acid Solvent B: Buffer: ACN (45:55 v/v) 3 Flow rate 1.2 ml/min 4 Detection wavelength 240 nm 5 Injection volume 20 µl 6 Temperature Ambient temperature

Table 1: The optimized chromatographic conditions for analysis of lopinavir and ritonavir.