Ritonavir is an antiretroviral drug from the protease inhibitor class used to treat HIV infection and AIDS. Ritonavir is very hydrophobic and non-ionizable and retains very long in reverse phase chromatography. Ribavirin is an anti-viral drug which is active against a number of DNA and RNA viruses. It is a member of the nucleoside antimetabolite drug, which makes it very hydrophilic. Ritonavir and Ribavarin are two drugs which are very different in their properties for HPLC separation. Very hydrophobic and very hydrophilic drugs are separated on Primesep N using Hydrophilic Interaction Chromatography.