Abstract: The lower end of an ion exchange column is provided with a rotatable valve member which, in a first position, supports resin material in the column and, in a second position, allows the resin material to drop out of the column. The valve member can include a sintered body which in the first position supports the resin material and permits drainage of reagents introduced into the column. On rotating the valve member into its second position the sintered body can fall out of the valve member to permit the resin material to fall out of the column through the valve member. A replacement sintered body can be dropped down the column on to the valve member and the column can be refilled with resin material for further use.