Chromatography

Chromatography is a continuously evolving scientific discipline or field "studying the formation, change, movement, and separation of multiple concentration zones of chemical compounds (analytes or particles) of the studied sample in a flow of mobile phase relative to selective influence of one or a number of solid/liquid stationary phases or sorbents."^[1] Components requiring separation join with the mobile phase — a gas or a liquid, for example — and pass through an immobile or stationary phase — a liquid or a solid. The components sorb or accumulate either in the stationary phase or at the border of where the phases interface, moving at different speeds based on sorptivity and forming a regular distribution.^[2] This distribution is measured with the help of a chromatograph, spectrophotometer, mass spectrometer, and/or other detector and output as a chromatogram, typically in graph form as a function of elution time.

Methods

Chromatographic separations were originally confined to colored plant pigments and dyes, but they quickly expanded to include colorless substances. Today, chromatographic methodology has expanded greatly with technological and scientific innovation, with a method for almost any type of analyte or particulate matter in the most minute of quantity.^[2]

Chromatography has numerous associated methods, dependent on the process-specific movement and type of mobile phase^[1]:

Methods of chromatography
Mobility or equilibria	Phase	Chromatography type
→	Liquid	Tswett (column), paper, thin-layer
→	Gas	Gas
→	Supercritical medium	Supercritical fluid
→	Electrical flow	Electro
↔	Sorbent liquid	Hypersorption, countercurrent, denuder
↓↑	Adsorption	Liquid-solid (gel), gas-solid, supercritical fluid-solid
↓↑	Chemisorption	Ion exchange, affinity, complex-forming
↓↑	Absorption (partition)	Liquid-liquid, gas-liquid
↓↑	Physical field	Field-flow fractionation
Equilibrium (isotherm)	Techniques, channel	Hyphenated techniques
Linear	Zone, column	One-dimensional
Non-linear	Frontal, slot	Multidimensional
Non-linear	Displacement, flat bed	Combined with spectral methods