PURITASTM BIO EXIMIUS C4 phases are bonded with Butyl groups and are fully end capped. They are recommended for compounds which are too strongly retained on C18 and C8 phases. PURITASTM BIO EXIMIUS C4 phases are available in particle sizes of 5, 10 and 15 microns for both analytical as well as preparative applications. These phase are widely used for larger molecules such as proteins with low to medium hydrophobicity. The improved high density bonding and full end capping makes it very suitable to general use and to separate or purify high molecular weight compounds, especially proteins. Because of the significant improvement in durability and acidic, alkalic resistance it can be used for extended period of time in acidic mobile phase condition and rinsed for recovery with NaOH containing buffer.