This type of chromatography relies on the binding of a reagent to the analyte molecules in a sample. The bound molecules are retained in the column, while the unbound analyte passes through the mobile phase. The stationary phase, typically agarose or porous glass beads, immobilizes the bonded molecules. Adjusting the pH or ionic strength of the binding ligand can modify the elution conditions. Biochemists frequently employ this technique for protein purification, where they bond the ligand tag, separate it, and then remove it to obtain the pure protein.