Capillary electrophoresis (CE), also known as high-efficiency capillary electrophoresis, is a type of liquid phase micro-separation analysis technology that uses capillary as the separation channel, high-voltage direct current electric field as the driving force, and various characteristics of the sample as the basis. CE can be used to analyze components ranging from organic ions to biological macromolecules such as proteins and nucleic acids. CE is another important development in analytical science after high-performance liquid chromatography. It advanced the analytical science and moved the analysis range from the micro level to the nano level, and enabled the single-cell analysis and even the single-molecule analysis. It can be used to analyze a variety of body fluid samples such as serum or plasma, urine, cerebrospinal fluid, and saliva.
Types of capillary electrophoresis
According to the principle of sample separation, the design of CE is mainly divided into 1) Capillary zone electrophoresis (CZE); 2) Capillary isotachophoresis (CITP); 3) Micellar electrokinetic capillary chromatography (MECC); 4) Capillary gel electrophoresis (CGE); 5) Capillary isoelectric focusing (CIEF).
CZE is the basic operating mode of HPCE. Generally, phosphate or borate buffers are used, and the experimental conditions including buffer concentration, pH, voltage, temperature, and modifiers (acetonitrile, methanol, etc.) are adjusted accordingly for separation and analysis of charged substances (drugs, proteins, peptides, etc.). CZE cannot be used to separate neutral substances.
MECC is a new type of liquid chromatography based on micellar solubilization and electrokinetic migration. MECC uses surfactants based on CZE to act as micellar phases. The solute has different partition coefficients in the water phase and micellar phase. Under the action of an electric field, the electroosmotic flow of the solution in the capillary and the electrophoresis of the micelles cause the micelles and the water phase to have different migration speeds. At the same time, the substances to be separated are distributed multiple times in the water phase and the micellar phase, and are separated under the dual effects of electroosmotic flow and this distribution process. MECC broadens the application range of CZE, is suitable for the separation of neutral substances, and can also distinguish chiral compounds. It can be used for the analysis of amino acids, peptides, small molecule substances, chiral substances, drug samples, and body fluid samples.
CITP uses a leading electrolyte and a subsequent electrolyte to form a discontinuous buffer system, which is separated based on the difference in electrophoretic mobility of the solute. CITP is often used for ionic substances (such as organic acids). It can be used for micro-preparation because it is suitable for capillary with a larger inner diameter. However, the spatial resolution of this method is poor.
CIEF is used for samples with zwitterions (proteins, peptides). The isoelectric point separation and detection of different components in the sample can be achieved by determining the isoelectric point of amphoteric substances.
CGE is separated according to the molecular weight of macromolecular substances, and is mainly used for the separation of proteins and nucleotide fragments.
In addition, there are capillary electrochromatography (CEC) and non-aqueous capillary electrophoresis (CNACE), which are used for the analysis of poorly water-soluble substances and difficult reactions in water.
Reference
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