Why is high concentration of NaCl used in ion-exchange chromatography for elution?

NaCl dissociates in Na+ and Cl- in solution. In anion-exchange chromatography, Cl- competes with negatively charged analytes to bind with positively charged stationary phase, thereby eluting the analytes. In the case of cation-exchange chromatography, Na+ will compete with the positively charged analytes to bind with the negatively charged column, also resulting in the elution of analytes.