S.No Conc of Internal standard (µg/ml) Area of Internal standard Conc of ritonavir (µg/ml) Conc of lopinavir (µg/ml) Area of ritonavir Area of lopinavir Response factor of ritonavir Response  factor of lopinavir 1 2 3 4 5   20   706763 10 20 30 40 50 40 80 120 160 200 180692 333938 484976 630074 796551 108837 313309 520991 766285 942405 0.255 0.472 0.686 0.891 1.092 0.182 0.499 0.582 1.013 1.092

Table 2: Linearity of the developed RP-HPLC method.