The packing of anion exchange column is a positively charged packing, which can adsorb anion and negatively charged substances (e.g., DNA) in the sample through charge interaction under low salt conditions. These negatively charged substances have different binding forces to the positively charged packing due to their different charge and molecular size. When the column sample is eluted with a gradient of chloride ions (usually a gradient of sodium chloride, e.g., a linear gradient from 100 mM sodium chloride to 1 M sodium chloride), the chloride ions compete with the bound substances for binding to the positively charged packing material, and as the concentration of the chloride ions continues to increase, the competition between the chloride ions becomes stronger and stronger, and the substances that have been bound to the packing material are eluted in order of weakest to strongest affinity, forming separate elution peaks, thus separating these substances. These substances can be separated from each other.

The cation exchange column is the opposite of a cation exchange column, where the column packing is negatively charged and the positively charged substances are eluted with sodium ions.