Normally an @[email protected] porous solid, which sorbs the liquid phase. The particle-size range of the support affects column efficiency and the pressure differential necessary to achieve a given flow rate. Modifications have been introduced for the achievement of special separations, in which the solid support is not @[email protected] but is an @[email protected] In capillary columns the inner wall of the column serves as the solid support and obviates the use of additional porous solids for this purpose.