wall effect - the consequence of the looser packing density near the walls of the rigid HPLC column. Mobile phase has a tendency to flow slightly faster near the wall because of the decreased permeability. The solute molecules that happen to be near the wall are carried along faster than the average of the solute band and, consequently, band spreading results.

WAX - weak anion exchanger. Ionizable groups such as primary, secondary, or tertiary amino groups on a packing are considered to be weak.

WCX - weak cation exchanger. Carboxylic groups on a packing are typical of a weak cation exchanger.