Complexation chromatography obtains selectivity from reversible formation of a coordination or host–guest complex between an analyte and a complexing species located in the stationary phase or mobile phase. Complex formation changes the analyte’s effective affinity, charge, or partition coefficient, and differences in equilibrium constants therefore produce different migration rates. In argentation chromatography, for example, immobilized or dissolved silver(I) forms reversible π-complexes with carbon–carbon multiple bonds, so retention varies with the number, geometry, and accessibility of unsaturated sites ^[1]. The general mode requires a chemically defined complexing agent, rapid and reversible complexation on the chromatographic timescale, and conditions that preserve the agent while allowing solute release. It differs from ordinary adsorption or partition chromatography because a discrete complexation equilibrium is the intended source of selectivity, and it excludes irreversible derivatization before injection. Ligand-exchange chromatography is a narrower metal-coordination form in which analytes exchange within a metal coordination sphere ^[2].