Editing Chromatography (section)

===Two-dimensional chromatography===
In some cases, the selectivity provided by the use of one column can be insufficient to provide resolution of analytes in complex samples. Two-dimensional chromatography aims to increase the resolution of these peaks by using a second column with different physico-chemical ([[chemical classification]]) properties.<ref name="Prebihalo-2018">{{cite journal | vauthors = Prebihalo SE, Berrier KL, Freye CE, Bahaghighat HD, Moore NR, Pinkerton DK, Synovec RE | title = Multidimensional Gas Chromatography: Advances in Instrumentation, Chemometrics, and Applications | journal = Analytical Chemistry | volume = 90 | issue = 1 | pages = 505–532 | date = January 2018 | pmid = 29088543 | doi = 10.1021/acs.analchem.7b04226 }}</ref><ref name="Stoll-2017">{{cite journal | vauthors = Stoll DR, Carr PW | title = Two-Dimensional Liquid Chromatography: A State of the Art Tutorial | journal = Analytical Chemistry | volume = 89 | issue = 1 | pages = 519–531 | date = January 2017 | pmid = 27935671 | doi = 10.1021/acs.analchem.6b03506 }}</ref> Since the mechanism of retention on this new solid support is different from the first dimensional separation, it can be possible to separate compounds by [[two-dimensional chromatography]] that are indistinguishable by one-dimensional chromatography. Furthermore, the separation on the second dimension occurs faster than the first dimension.<ref name="Prebihalo-2018" /> An example of a TDC separation is where the sample is spotted at one corner of a square plate, developed, air-dried, then rotated by 90° and usually redeveloped in a second solvent system.

Two-dimensional chromatography can be applied to GC or LC separations.<ref name="Prebihalo-2018" /><ref name="Stoll-2017" /> The heart-cutting approach selects a specific region of interest on the first dimension for separation,<ref>{{cite journal | vauthors = Tranchida PQ, Sciarrone D, Dugo P, Mondello L | title = Heart-cutting multidimensional gas chromatography: a review of recent evolution, applications, and future prospects | journal = Analytica Chimica Acta | volume = 716 | pages = 66–75 | date = February 2012 | pmid = 22284880 | doi = 10.1016/j.aca.2011.12.015 | url = http://www.sciencedirect.com/science/article/pii/S0003267011016801 | series = A selection of papers presented at the 12th International Symposium on Extraction Technologies (ExTech 2010) | bibcode = 2012AcAC..716...66T }}</ref> and the comprehensive approach uses all analytes in the second-dimension separation.<ref name="Prebihalo-2018" /><ref name="Stoll-2017" />