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 (HILIC). 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.