Topics - Silanol
Silanol is a name that has been given (and is generally accepted) to an hydroxyl group that is attached to a silicon atom. In chromatography the term silanol usually pertains to the hydroxyl groups attached to the surface of silica gel. It is the silanol groups on the silica gel surface that are reacted with appropriate silyl, or silane reagents to form the ‘so called’ bonded phases. The silanol groups have very strong polar interactivity
and are responsible for the strong polar character of silica gel. Normally the silanol groups are hydrogen bonded to water and constitute at least part of the strongly held water that is only lost when the gel is heated to 200 C. The hydrated silanol groups will extract polar components from a mobile phase mixture and form a layer of the polar solvent on the surface (e.g. a mobile phase consisting of 2%ethyl acetate in n-heptane). Under such circumstances (at least for the less retained solutes) competitive polar
distribution takes place between pure ethyl acetate on the silica gel surface and a very dilute solution of ethyl acetate in the mobile phase mixture. Superimposed on the polar
interactive competition will be the dispersive
iteractive competition resulting from the dispersive properties
of the silica gel and the n-heptane.