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| '''Capillary electrophoresis''' ('''CE'''), also known as capillary zone electrophoresis (CZE), can be used to separate ionic species by their charge and frictional forces and hydrodynamic radius. In traditional [[electrophoresis]], electrically charged analytes move in a [[conductive]] [[liquid]] medium under the influence of an [[electric field]]. Introduced in the 1960s, the technique of capillary electrophoresis (CE) was designed to separate species based on their size to charge ratio in the interior of a small capillary filled with an [[electrolyte]].
| | {{wikipedia::Capillary electrophoresis}} |
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| == Instrumentation==
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| The instrumentation needed to perform capillary electrophoresis is relatively simple. A basic [[schematic]] of a capillary electrophoresis system is shown in ''Figure 1''. The system's main components are a sample vial, source and destination vials, a capillary, [[electrode]]s, a high-[[voltage]] [[power supply]], a detector, and a data output and handling device. The source vial, destination vial and capillary are filled with an electrolyte such as an aqueous buffer solution. To introduce the sample, the capillary inlet is placed into a vial containing the sample and then returned to the source vial (sample is introduced into the capillary via [[capillary action]], pressure, or siphoning). The migration of the analytes is then initiated by an electric field that is applied between the source and destination vials and is supplied to the electrodes by the high-voltage power supply. It is important to note that all ions, positive or negative, are pulled through the capillary in the same direction by [[electroosmotic flow]], as will be explained. The analytes separate as they migrate due to their electrophoretic mobility, as will be explained, and are detected near the outlet end of the capillary. The output of the detector is sent to a data output and handling device such as an [[integrator]] or [[computer]]. The data is then displayed as an electropherogram, which reports detector response as a function of [[time]]. Separated [[chemical compound]]s appear as peaks with different migration times in an electropherogram.<ref name="Baker">Skoog, D.A.; Holler, F.J.; Crouch, S.R "Principles of Instrumental Analysis" 6th ed. Thomson Brooks/Cole Publishing: Belmont, CA '''2007'''.</ref>
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| [[Image:Capillaryelectrophoresis.gif|frame|Figure 1: Diagram of capillary electrophoresis system]]
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| ==Detection==
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| Separation by capillary electrophoresis can be detected by several detection devices. The majority of commercial systems use [[UV]] or UV-Vis [[absorbance]] as their primary mode of detection. In these systems, a section of the capillary itself is used as the detection cell. The use of on-tube detection enables detection of separated analytes with no loss of resolution. In general, capillaries used in capillary electrophoresis are coated with a [[polymer]] for increased stability. The portion of the capillary used for UV detection, however, must be optically transparent. Bare capillaries can break relatively easily and, as a result, capillaries with transparent coatings are available to increase the stability of the cell window. The [[path length]] of the detection cell in capillary electrophoresis (~ 50 [[micrometre|micrometers]]) is far less than that of a traditional UV cell (~ 1 cm). According to the [[Beer-Lambert law]], the sensitivity of the detector is proportional to the path length of the cell. To improve the sensitivity, the path length can be increased, though this results in a loss of resolution. The capillary tube itself can be expanded at the detection point, creating a "bubble cell" with a longer path length or additional tubing can be added at the detection point as shown in ''figure 2''. Both of these methods, however, will decrease the resolution of the separation.<ref name="Cucino">Skoog, D.A.; Holler, F.J.; Crouch, S.R "Principles of Instrumental Analysis" 6th ed. Chapter 30 Thomson Brooks/Cole Publishing: Belmont, CA '''2007'''.</ref>
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| [[Image:Extendedpathlength.gif|frame|Figure 2: Techniques for increasing the pathlength of the capillary: a.) a bubble cell and b.) a z-cell (additional tubing).<ref name="Baker"/>]]
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| [[Fluorescence]] detection can also be used in capillary electrophoresis for samples that naturally fluoresce or are chemically modified to contain [[fluorescent tag]]s. This mode of detection offers high sensitivity and improved selectivity for these samples, but cannot be utilized for samples that do not fluoresce. The set-up for fluorescence detection in a capillary electrophoresis system can be complicated. The method requires that the light beam be focused on the capillary, which can be difficult for many light sources.<ref name="Cucino"/> [[Laser]]-induced fluorescence has been used in CE systems with detection limits as low as 10<sup>−18</sup> to 10<sup>−21</sup> mol. The sensitivity of the technique is attributed to the high [[Irradiance|intensity]] of the [[wiktionary:incident|incident]] light and the ability to accurately focus the light on the capillary.<ref name="Baker"/>
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| In order to obtain the identity of sample components, capillary electrophoresis can be directly coupled with [[mass spectrometer]]s or [[Surface Enhanced Raman Spectroscopy]] (SERS). In most systems, the capillary outlet is introduced into an ion source that utilizes [[electrospray ionization]] (ESI). The resulting ions are then analyzed by the mass spectrometer. This set-up requires [[Volatility (chemistry)|volatile]] buffer solutions, which will affect the range of separation modes that can be employed and the degree of resolution that can be achieved.<ref name="Cucino"/>
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| The measurement and analysis are mostly done with a specialized [http://www.labimage.com gel analysis software].
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| For CE-SERS, capillary electrophoresis [[eluant]]s can be deposited onto a SERS-active substrate. Analyte retention times can be translated into spatial distance by moving the SERS-active substrate at a constant rate during capillary electrophoresis. This allows the subsequent spectroscopic technique to be applied to specific eluants for identification with high sensitivity. SERS-active substrates can be chosen that do not interfere with the spectrum of the analytes.<ref name="Lin">Lin H.; Natan, M.; Keating, C. ''Anal. Chem''. '''2000''', ''72'', 5348-5355.</ref>
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| ==See also==
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| * [[Affinity electrophoresis]]
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| * [[Kinetic capillary electrophoresis]]
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| ==Bibliography==
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| *Terabe, S.; Otsuka, K.; Ichikawa, K.; Tsuchiya, A.; Ando, T. ''Anal. Chem''. '''1984''', ''56'', 111.
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| *Terabe, S.; Otsuka, K.; Ichikawa, K.; Tsuchiya, A.; Ando, T. ''Anal. Chem''. '''1984''', ''56'', 113.
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| *Foley, J.P. ''Anal. Chem''. '''1990''', ''62'', 1302.
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| *Carretero, A.S.; Cruces-Blanco, C.; Ramirez, S.C.; Pancorbo, A.C.; Gutierrez, A.F. ''J. Agric. Food. Chem''. '''2004''', ''52'', 5791.
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| *Cavazza, A.; Corradini, C.; Lauria, A.; Nicoletti, I. ''J. Agric. Food Chem''. '''2000''', ''48'', 3324.
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| *Rodrigues, M.R.A.; Caramao, E.B.; Arce, L.; Rios, A.; Valcarcel, M. ''J. Agric. Food Chem''. '''2002''', ''50'', 4215.
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| ==External links==
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| *CE animations [http://www.shsu.edu/%7Echm_tgc/sounds/sound.html]
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| *CE Primer for Beginners & Experts [http://www.mtc-usa.com/ce.asp]
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| ==Notes== | | ==Notes== |
| | | This article is a direct transclusion of [https://en.wikipedia.org/wiki/Capillary_electrophoresis the Wikipedia article] and therefore may not meet the same editing standards as LIMSwiki. |
| The bulk of this article is reused from [http://en.wikipedia.org/wiki/Capillary_electrophoresis the Wikipedia article].
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| ==References==
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| {{Reflist}}
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| <!---Place all category tags here--> | | <!---Place all category tags here--> |
| | [[Category:Articles transcluded from other wikis]] |
| [[Category:Chromatography]] | | [[Category:Chromatography]] |
| [[Category:Scientific techniques]] | | [[Category:Scientific techniques]] |
