Silica Gel C18 is a kind of silica gel which is on the basis of normal phase silica gel (ordinary silica gel, the functional group is OH), and OH is substituted by OR (R is a hydrocarbon chain, or called a carbon chain, CH) in a chemical reaction.

As silica gel C18 is long chain alkyl bonded phase, which has a higher carbon content and better hydrophobicity, and has a greater ability to adapt to various types of biological macromolecules, so it mainly used for separating those samples which has strong polar and complex composition.