Editing Chromatography (section)

=== Hydrodynamic chromatography ===
Hydrodynamic chromatography (HDC) is derived from the observed phenomenon that large droplets move faster than small ones.<ref>{{cite journal | vauthors = Song H, Tice JD, Ismagilov RF | title = A microfluidic system for controlling reaction networks in time | journal = Angewandte Chemie | volume = 42 | issue = 7 | pages = 768–72 | date = February 2003 | pmid = 12596195 | doi = 10.1002/anie.200390203 }}</ref> In a column, this happens because the [[center of mass]] of larger droplets is prevented from being as close to the sides of the column as smaller droplets because of their larger overall size.<ref>{{cite journal|last1=Small|first1=Hamish|last2=Langhorst|first2=Martin A. |date=1982-07-01|title=Hydrodynamic Chromatography|journal=Analytical Chemistry|volume=54|issue=8|pages=892A–898A|doi=10.1021/ac00245a724|issn=0003-2700}}</ref> Larger droplets will elute first from the middle of the column while smaller droplets stick to the sides of the column and elute last. This form of chromatography is useful for separating analytes by [[molar mass]] (or molecular mass), size, shape, and structure when used in conjunction with [[Scattering|light scattering]] detectors, [[viscometer]]s, and [[refractometer]]s.<ref>{{cite journal | vauthors = Brewer AK, Striegel AM | title = Characterizing string-of-pearls colloidal silica by multidetector hydrodynamic chromatography and comparison to multidetector size-exclusion chromatography, off-line multiangle static light scattering, and transmission electron microscopy | journal = Analytical Chemistry | volume = 83 | issue = 8 | pages = 3068–75 | date = April 2011 | pmid = 21428298 | doi = 10.1021/ac103314c }}</ref> The two main types of HDC are open tube and [[Packed bed|packed column]]. Open tube offers rapid separation times for small particles, whereas packed column HDC can increase resolution and is better suited for particles with an average molecular mass larger than <math>10^5</math> [[Dalton (unit)|daltons]].<ref name="Stegeman-1994">{{cite journal|last1=Stegeman|first1=Gerrit.|last2=van Asten|first2=Arian C.|last3=Kraak|first3=Johan C.|last4=Poppe|first4=Hans.|last5=Tijssen|first5=Robert |date=1994|title=Comparison of Resolving Power and Separation Time in Thermal Field-Flow Fractionation, Hydrodynamic Chromatography, and Size-Exclusion Chromatography|journal=Analytical Chemistry|language=en|volume=66|issue=7|pages=1147–1160|doi=10.1021/ac00079a033|issn=0003-2700|url=http://dare.uva.nl/personal/pure/en/publications/comparison-of-resolving-power-and-separation-time-in-thermal-fieldflow-fractionation-hydrodynamic-chromatography-and-sizeexclusion-chromatography(dbf9005b-3cd3-4824-810e-c15cccabf1ce).html}}</ref> HDC differs from other types of chromatography because the separation only takes place in the interstitial volume, which is the volume surrounding and in between particles in a packed column.<ref>{{cite journal|last=Small|first=Hamish|date=1974-07-01|title=Hydrodynamic chromatography a technique for size analysis of colloidal particles|journal=Journal of Colloid and Interface Science|language=en|volume=48|issue=1|pages=147–161|doi=10.1016/0021-9797(74)90337-3|bibcode=1974JCIS...48..147S|issn=0021-9797}}</ref>

HDC shares the same order of elution as [[Size-exclusion chromatography|Size Exclusion Chromatography]] (SEC) but the two processes still vary in many ways.<ref name="Stegeman-1994" /> In a study comparing the two types of separation, Isenberg, Brewer, Côté, and Striegel use both methods for [[polysaccharide]] characterization and conclude that HDC coupled with [[multiangle light scattering]] (MALS) achieves more accurate [[molar mass distribution]] when compared to off-line MALS than SEC in significantly less time.<ref name="Isenberg-2010">{{cite journal | vauthors = Isenberg SL, Brewer AK, Côté GL, Striegel AM | title = Hydrodynamic versus size exclusion chromatography characterization of alternan and comparison to off-line MALS | journal = Biomacromolecules | volume = 11 | issue = 9 | pages = 2505–11 | date = September 2010 | pmid = 20690593 | doi = 10.1021/bm100687b }}</ref> This is largely due to SEC being a more destructive technique because of the pores in the column degrading the analyte during separation, which tends to impact the mass distribution.<ref name="Isenberg-2010" /> However, the main disadvantage of HDC is low [[Resolution (chromatography)|resolution]] of analyte peaks, which makes SEC a more viable option when used with chemicals that are not easily degradable and where rapid elution is not important.<ref name="Striegel-2012">{{cite journal | vauthors = Striegel AM, Brewer AK | title = Hydrodynamic chromatography | journal = Annual Review of Analytical Chemistry | volume = 5 | issue = 1 | pages = 15–34 | date = 2012-07-19 | pmid = 22708902 | doi = 10.1146/annurev-anchem-062011-143107 | bibcode = 2012ARAC....5...15S }}</ref>

HDC plays an especially important role in the field of [[microfluidics]]. The first successful apparatus for HDC-on-a-chip system was proposed by Chmela, et al. in 2002.<ref name="Chmela-2002">{{cite journal | vauthors = Chmela E, Tijssen R, Blom MT, Gardeniers HJ, van den Berg A | title = A chip system for size separation of macromolecules and particles by hydrodynamic chromatography | journal = Analytical Chemistry | volume = 74 | issue = 14 | pages = 3470–5 | date = July 2002 | pmid = 12139056 | doi = 10.1021/ac0256078 | s2cid = 6948037 | url = https://ris.utwente.nl/ws/files/6705845/Chmela02chip.pdf }}</ref> Their design was able to achieve separations using an 80&nbsp;mm long channel on the timescale of 3 minutes for particles with diameters ranging from 26 to 110&nbsp;nm, but the authors expressed a need to improve the retention and [[Dispersion (chemistry)|dispersion]] parameters.<ref name="Chmela-2002" /> In a 2010 publication by Jellema, Markesteijn, Westerweel, and Verpoorte, implementing HDC with a recirculating bidirectional flow resulted in high resolution, size based separation with only a 3&nbsp;mm long channel.<ref>{{cite journal | vauthors = Jellema LJ, Markesteijn AP, Westerweel J, Verpoorte E | title = Tunable hydrodynamic chromatography of microparticles localized in short microchannels | journal = Analytical Chemistry | volume = 82 | issue = 10 | pages = 4027–35 | date = May 2010 | pmid = 20423105 | doi = 10.1021/ac902872d }}</ref> Having such a short channel and high resolution was viewed as especially impressive considering that previous studies used channels that were 80&nbsp;mm in length.<ref name="Chmela-2002" /> For a biological application, in 2007, Huh, et al. proposed a microfluidic sorting device based on HDC and gravity, which was useful for preventing potentially dangerous particles with diameter larger than 6 microns from entering the bloodstream when injecting [[contrast agent]]s in [[Medical ultrasound|ultrasounds]].<ref>{{cite journal | vauthors = Huh D, Bahng JH, Ling Y, Wei HH, Kripfgans OD, Fowlkes JB, Grotberg JB, Takayama S | display-authors = 6 | title = Gravity-driven microfluidic particle sorting device with hydrodynamic separation amplification | journal = Analytical Chemistry | volume = 79 | issue = 4 | pages = 1369–76 | date = February 2007 | pmid = 17297936 | pmc = 2527745 | doi = 10.1021/ac061542n }}</ref> This study also made advances for environmental sustainability in microfluidics due to the lack of outside electronics driving the flow, which came as an advantage of using a gravity based device.[[File:GCxGC-TOFMS Analytical Dept Chemical Faculty GUT Gdansk.jpg |thumb|upright| Two-dimensional chromatograph GCxGC-TOFMS at [[Faculty of Chemistry, Gdańsk University of Technology|Chemical Faculty]] of [[Gdańsk University of Technology|GUT]] [[Gdańsk]], [[Poland]], 2016]]