Ion-exchange chromatography

Ion-exchange chromatography separates charged molecules by reversible binding to oppositely charged groups on a stationary material, then eluting them under changing conditions.

Stationary phase: The fixed material in a chromatography system that interacts with compounds as a mobile phase passes through. Its charged groups provide the exchange sites that retain sample ions.
Protein purification: The isolation of a target protein from a mixture of biological molecules. Proteins differ in net charge, allowing selective retention at a chosen pH.
Acid–base equilibrium: The balance between protonated and deprotonated forms of acids and bases in solution. It determines how pH changes the charge of solutes and some exchange groups.
Size-exclusion chromatography: A chromatography method that separates molecules by their access to pores in a stationary phase. It sorts primarily by molecular size rather than charge-dependent binding.
Mobile phase: The fluid that carries sample compounds through a chromatography system. Its salt concentration and pH can weaken binding and release retained ions.
Amino acid analysis: The identification and quantification of amino acids in a sample. Ion-exchange columns can resolve amino acids before detection and measurement.
Isoelectric point: The pH at which a molecule has zero net electrical charge. Protein binding changes around this pH as its net charge shifts.
Reversed-phase chromatography: A chromatography method that separates compounds by hydrophobic interactions with a nonpolar stationary phase. Its retention is driven chiefly by hydrophobicity, not ionic attraction.
Cation-exchange chromatography: A form of ion-exchange chromatography in which negatively charged stationary groups retain positively charged solutes. It separates cations through attraction to negatively charged exchange sites.
Water softening: The removal of calcium and magnesium ions from water, commonly by exchanging them for sodium ions. It applies cation exchange to reduce the ions responsible for hardness.

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