= Chromatography
{wiki}
<Chromatography> separates components of a <mixture> through different migration rates in contact with a <chromatographic stationary phase> while a <chromatographic mobile phase> transports them. <Liquid chromatography> describes the physical state of the transporting phase; <size-exclusion chromatography> describes a separation mechanism. Classification by phase and classification by mechanism answer different questions. In ideal <size-exclusion chromatography>, differential access to liquid-filled pores replaces binding as the source of differential migration.
In many other forms of <chromatography>, a <solute> repeatedly leaves the <chromatographic mobile phase> and returns to it. Reversible <adsorption> holds it at a surface; partition distributes it between the <chromatographic mobile phase> and an immobilized liquid <chromatographic stationary phase>. Spending more time stationary means less progress with the moving fluid. Two initially overlapping components can therefore emerge as separate bands without either being permanently trapped. <Chromatography> is useful both for comparing a sample with reference substances and for collecting separated components; a visible band need not contain just one substance.
Relative retention belongs to the sample together with the chosen <chromatographic stationary phase>, <chromatographic mobile phase>, <eluent> composition, and <temperature>. Changing these conditions can change the separation order. <Chemical polarity> helps explain interactions in some systems but is not a universal ranking rule. In <thin-layer chromatography>, a spot's <TLC retardation factor> is consequently conditional evidence about identity, rather than a fixed identifier intrinsic to a <molecule>.
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