In biochemistry, capillary electrophoresis is a technique that is used to separate out molecules by their size and electrical charge. It is also often called capillary zone electrophoresis or capillary gel electrophoresis. Capillary electrophoresis analysis relies on the principle that molecules possess differing electrical charges and differing weights. Thus, when molecules in a substrate are exposed to an electrical field, different molecules will move in different directions and at differing speeds within the substrate.
When a substrate has an electrical field applied to it by means of one electrode at either end of the field, positively charged molecules will move towards the negative electrode, and negatively charged molecules will move towards the positive electrode. The relative speed at which the molecule will move through the substrate is determined by a characteristic known as the hydrodynamic size of the molecule. The hydrodynamic size of a molecule depends on two factors, its mass, and the strength of its positive or negative charge. A large molecule with a strong positive charge will tend to move relatively rapidly towards the negative electrode in an electrical field. A small molecule with a weak negative charge will tend to move much more slowly towards the positive electrode in an electrical field.
Once a charge has been applied to a sample for a set length of time, and the molecules being analyzed have been separated, it is necessary to show the scientist where the different molecules are located in the substrate. In many modern capillary electrophoresis systems this is achieved with ultraviolet (UV) light. The UV illumination can show a user the physical path that has been traced by a molecule, or set of molecules, through the substrate. In other systems, the molecules to be analyzed are first treated with chemicals to give them a fluorescent property. Fluorescent detection methods can be very sensitive, but are not suitable for every type of molecule.
The applications of capillary electrophoresis in science are many and varied. Capillary electrophoresis sequencing is a process, used particularly by geneticists, in which capillary electrophoresis is used to analyze molecules of the genetic material Deoxyribo Nucleic Acid (DNA). Food scientists may use capillary electrophoresis protein analysis to determine the different protein content characteristics of food. In medical research, this process has many applications, such as the analysis of antibodies, and the study of how they bind to other molecules.