Editing Chromatography (section)

==Techniques by physical state of mobile phase==
===Gas chromatography===<!-- This section is linked from [[Biodiesel]] -->
{{further|Gas chromatography}}
Gas chromatography (GC), also sometimes known as gas-liquid chromatography, (GLC), is a separation technique in which the mobile phase is a gas. Gas chromatographic separation is always carried out in a column, which is typically "packed" or "capillary".  Packed columns are the routine workhorses of gas chromatography, being cheaper and easier to use and often giving adequate performance.   Capillary columns generally give far superior resolution and although more expensive are becoming widely used, especially for complex mixtures. Further, capillary columns can be split into three classes: porous layer open tubular (PLOT), wall-coated open tubular (WCOT) and support-coated open tubular (SCOT) columns. PLOT columns are unique in a way that the stationary phase is adsorbed to the column walls, while WCOT columns have a stationary phase that is chemically bonded to the walls. SCOT columns are in a way the combination of the two types mentioned in a way that they have support particles adhered to column walls, but those particles have liquid phase chemically bonded onto them.<ref>{{cite book |last1=Rahman |first1=M. |last2=El-Aty |first2=A.M.A. |last3=Choi |first3=J.-H. |last4=Shin |first4=H.-C. |last5=Shin |first5=S.-C. |last6=Shim |first6=J.-H. |date=November 2015 |title= Analytical Separation Science |pages=823–834 |chapter=Chapter 3 Basic Overview on Gas Chromatography Columns |publisher=John Wiley & Sons |isbn=9783527333745}}</ref> Both types of column are made from non-adsorbent and chemically inert materials. Stainless steel and glass are the usual materials for packed columns and quartz or fused silica for capillary columns.

Gas chromatography is based on a [[partition equilibrium]] of analyte between a solid or viscous liquid stationary phase (often a liquid silicone-based material) and a mobile gas (most often helium). The stationary phase is adhered to the inside of a small-diameter (commonly 0.53 – 0.18mm inside diameter) glass or fused-silica tube (a capillary column) or a solid matrix inside a larger metal tube (a packed column). It is widely used in [[analytical chemistry]]; though the high temperatures used in GC make it unsuitable for high molecular weight biopolymers or proteins (heat denatures them), frequently encountered in [[biochemistry]], it is well suited for use in the [[petrochemical]], [[environmental monitoring]] and [[Environmental remediation|remediation]], and [[Chemical industry|industrial chemical]] fields. It is also used extensively in chemistry research.

===Liquid chromatography===
[[File:Preparative HPLC.svg|thumb|upright=1.8|Preparative HPLC apparatus]]
Liquid chromatography (LC) is a separation technique in which the mobile phase is a liquid. It can be carried out either in a column or a plane. Present day liquid chromatography that generally utilizes very small packing particles and a relatively high pressure is referred to as [[high-performance liquid chromatography]].

In HPLC the sample is forced by a liquid at high pressure (the mobile phase) through a column that is packed with a stationary phase composed of irregularly or spherically shaped particles, a [[Monolithic HPLC column|porous monolithic layer]], or a porous membrane. Monoliths are "sponge-like chromatographic media"<ref name="González-González-2020"/> and are made up of an unending block of organic or inorganic parts. HPLC is historically divided into two different sub-classes based on the polarity of the mobile and stationary phases. Methods in which the stationary phase is more polar than the mobile phase (e.g., [[toluene]] as the mobile phase, silica as the stationary phase) are termed normal phase liquid chromatography (NPLC) and the opposite (e.g., water-methanol mixture as the mobile phase and C18 ({{chem name|[[octadecylsilyl]]}}) as the stationary phase) is termed reversed phase liquid chromatography (RPLC).

===Supercritical fluid chromatography===
{{main|Supercritical fluid chromatography}}

Supercritical fluid chromatography is a separation technique in which the mobile phase is a fluid above and relatively close to its critical temperature and pressure.