After the last solute has been eluted, it is necessary to strip the displacer from the column.  Since the displacer was chosen for high affinity, this can pose a challenge.  On reverse-phase materials, a wash with a high percentage of organic solvent may suffice. Large pH shifts are also often employed.  One effective strategy is to remove the displacer by chemical reaction; for instance if hydrogen ion was used as displacer it can be removed by reaction with hydroxide, or a polyvalent metal ion can be removed by reaction with a chelating agent. For some matrices, reactive groups on the stationary phase can be titrated to temporarily eliminate the binding sites, for instance weak-acid ion exchangers or chelating resins can be converted to the protonated form. For gel-type ion exchangers, selectivity reversal at very high ionic strength can also provide a solution.  Sometimes the displacer is specifically designed with a titratable functional group to shift its affinity.  After the displacer is washed out, the column is washed as needed to restore it to its initial state for the next run.