Capillary electrophoresis (CE)
Capillary electrophoresis (CE) is an analytical technique used to separate the components of a mixture by applying an electrical field within a narrow tube known as a capillary. This method relies on the natural electrical charges of molecules, allowing them to be separated based on their charge and size. When an electric field is applied, positively charged molecules move toward the negatively charged cathode, while negatively charged molecules migrate towards the positively charged anode. The unique structure of the capillary enables differentiation by size, as larger molecules encounter more friction against the capillary walls and move more slowly compared to smaller molecules.
CE is particularly significant in various scientific fields, with one of its most notable applications being in DNA fingerprinting, where it aids forensic scientists in analyzing DNA samples. The technique is also widely used in pharmaceutical analysis to characterize drugs and separate proteins. Although the foundational concepts of CE were explored as early as the late 19th century, advancements in its practical application did not gain traction until the latter half of the 20th century. Today, CE is recognized for producing rapid and high-resolution results, making it a preferred choice in laboratories worldwide for molecular separation tasks.
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Capillary electrophoresis (CE)
Capillary electrophoresis (CE) is a method of separating the components of a mixture using an electrical field. Unlike other forms of electrophoresis, CE is specifically carried out with the use of a narrow tube called a capillary. In practice, CE is an analytic technique in which ions are separated through the application of applied voltage. Essentially, CE allows for the separation of molecules based on electrical charge and size. CE has a variety of practical purposes, the most notable of which being the key role it plays in DNA fingerprinting. CE can also be used in drug analysis, protein characterization, and more. The history of CE dates back as far as the late nineteenth century, and instruments for performing CE have been available commercially since the late 1980s. Given the ease with which it can be carried out, CE is a reliable and relatively simple means of separating molecules for analytical purposes that is used in laboratories around the world.
Background
Scientists first began to experiment with CE in the late nineteenth century. Most of these early experiments were conducted with the use of U-shaped glass tubes and various gel and free solutions. Swedish biochemist Arne Tiselius made the first major breakthrough in the development of electrophoresis when he conducted an experiment that showed the separation of proteins in free solutions in 1930. His work went all but unnoticed, however, until fellow Swedish scientist Stellan Hjertén introduced the idea of using capillaries as part of the electrophoresis process in the 1960s. Even with this critical development, CE generated little interest in the broader scientific community until James W. Jorgenson and Krynn DeArman Lukacs later published papers that demonstrated CE’s ability to perform molecular separations that were previously thought impossible. Although it took decades for CE to gain widespread recognition, it eventually garnered a great deal of interest among scientists, primarily because of how it improved upon traditional modes of electrophoresis and made the overall process more efficient and more reliable. Although its use has seen some fluctuation over time, CE continues to be a prevalent method of separating molecules.
The underlying principles of CE arise from basic molecular science. All molecules can be positively or negatively charged. If the numbers of positive and negative charges are the same, the charges cancel each other out, and the molecule is left with a neutral charge. In the event that they have the freedom to move, charged particles will always move toward a region with an opposing charge. Electrophoresis takes advantage of this fact, using the natural attraction of charged particles to regions of opposing charge as a means of separating particles by charge. The addition of a capillary in CE adds another dimension to the process, allowing particles to be separated by size as well as charge. Among the different types of electrophoresis that can be used to separate particles, CE is often the preferred method because it provides the fastest results and yields high-resolution separation. CE is also favored because it allows for the use of a wide range of detection methods.
Overview
CE is a form of electrophoresis, which itself is a method of separating molecules through the use of an electrical field. Electrophoresis relies on the natural electrical charges of various particles and uses electricity to separate these particles based on their charges. Electrophoresis is carried out with the aid of a pair of electrodes, including a positively charged anode and a negatively charged cathode. Because molecules can have a negative, positive, or neutral charge, different molecules can be drawn to either the anode or cathode when an electrical field is applied. Simply put, this means that positively charged molecules will be drawn to the cathode, while negatively charged molecules will be drawn to the anode. In the event that some sort of filter is placed in the path of the molecules being drawn toward one electrode or the other, the molecules can also be separated by size. This key concept is what makes CE different from standard electrophoresis. In CE, molecules are separated with the use of both an electrical field and a kind of small, narrow tube called a capillary.
The process of CE is relatively simple. Essentially, a capillary that is open on both ends is situated such that each end is in a separate receptacle that contains a buffer. A buffer is a substance that is used to carry molecules. In CE, the buffer is typically some sort of electrolytic solution. More often than not, the buffer has a positive charge and the capillary walls have a negative charge. This allows molecules to flow evenly through the capillary when an electrical field is applied. The receptacles that hold the buffer and the molecules that are to be separated also contain electrodes, with one housing the anode and the other housing the cathode. These electrodes are connected to a power source. When the electricity is turned on, the molecules begin to separate. While the positively charged molecules are drawn through the capillary toward the cathode, the negatively charged molecules remain attracted to the anode. If any molecules with a neutral charge exist, they will follow the positively charged particles to the cathode at a lower rate of speed. Thus, the various molecules are separated based on their electrical charge. In addition, the capillary itself helps to separate the molecules by size. The larger a molecule is, the slower it will move through the capillary due to increased friction between the molecule and the capillary walls. Smaller molecules experience less friction from contact with the capillary walls and therefore complete their journey to the cathode more quickly.
CE has many practical purposes. The most notable of these is tied to the process of DNA fingerprinting. In this context, CE can be used to separate amplified, or copied, DNA in order to create a high-resolution map of the DNA in question. This technique is most often used by forensic scientists seeking to use DNA evidence to solve crimes. CE is also used in the pharmaceutical industry as a method of analyzing various drugs and other compounds. Another common use of CE involves separating amphoteric proteins that react chemically as either an acid or a base. By utilizing CE in this manner, scientists can separate and identify different proteins.
Bibliography
“Advantages and Disadvantages of Capillary Electrophoresis.” Chromatography Today, 3 Nov. 2014, www.chromatographytoday.com/news/electrophoretic-separations/35/breaking-news/advantages-and-disadvantages-of-capillary-electrophoresis/32342. Accessed 9 Jan. 2019.
“Basic Theory and Introduction.” Microsolv Technology Corporation, mtc-usa.com/cebasic. Accessed 9 Jan. 2019.
“Capillary Electrophoresis.” LibreTexts, 28 Nov. 2017, chem.libretexts.org/Bookshelves/Analytical‗Chemistry/Supplemental‗Modules‗(Analytical‗Chemistry)/Instrumental‗Analysis/Capillary‗Electrophoresis. Accessed 9 Jan. 2019.
“Capillary Electrophoresis: An Attractive Technique for Chiral Separations.” Chromatography Today, 6 June 2013, www.chromatographytoday.com/article/electrophoretic-separations/35/cari‗e‗snger‗van‗de‗griend‗12‗ylva‗hedeland‗2‗curt‗pettersson‗2/capillary‗electrophoresis‗an‗attractive‗technique‗for‗chiral‗separations/1427. Accessed 9 Jan. 2019.
Carreras, Hector Zamora. "An Introduction to Capillary Electrophoresis: Theory, Practice, and Applications." Technology Network, 19 Sept. 2023, www.technologynetworks.com/analysis/articles/an-introduction-to-capillary-electrophoresis-theory-practice-and-applications-378737. Accessed 6 Nov. 2024.
“Introduction to Capillary Electrophoresis.” Prince Technologies, www.princetechnologies.eu/products/ce-systems/ce-technologies/ce-introduction/. Accessed 9 Jan. 2019.
Petersen, J.R., and A.A. Mohammad, editors. Clinical and Forensic Application of Capillary Electrophoresis.Humana Press, 2001.
Reed, Darla. “What Is Capillary Electrophoresis?” Study.com, study.com/academy/lesson/what-is-capillary-electrophoresis.html. Accessed 9 Jan. 2019.
“What Is Capillary Electrophoresis?” Chromatography Today, 8 Nov. 2014, www.chromatographytoday.com/news/electrophoretic-separations/35/breaking-news/what-is-capillary-electrophoresis/32375. Accessed 9 Jan. 2019.