Electrophoresis

The charged particles move toward the electrode opposite to the electric field under the action of an electric field, which is called electrophoresis (EP). A technique that uses separation of charged particles in an electric field to achieve separation is called electrophoresis.

Electrophoresis

Under certain conditions, the distance (ie, mobility) of charged particles per unit time under the action of the unit electric field strength is constant, which is the physicochemical characteristic constant of the charged particles. Different charged particles have different charges, or have the same charge but different charge-to-mass ratios, and are electrophoresed in the same electric field. After a certain period of time, they are separated from each other due to different moving distances. The separation distance is proportional to the voltage of the applied electric field and the electrophoresis time.

Under the action of an external DC power source, the colloidal particles move in a direction toward the cathode or the anode in a dispersion medium. This phenomenon is called electrophoresis. Separation of substances by electrophoresis is also called electrophoresis. The colloid has an electrophoresis phenomenon, which proves that the particles of the colloid are charged. The nature of various colloidal particles is different, they adsorb different ions, so they have different charges.

Law of charge movement

The electrical properties of the colloidal particles can be determined by electrophoresis, the colloidal particles moving toward the anode are negatively charged, and the colloidal particles moving toward the cathode are positively charged.

Generally, colloidal particles such as metal hydroxides and metal oxides adsorb cations and are positively charged; colloidal particles such as non-metal oxides and non-metal sulfides adsorb anions and are negatively charged.

Therefore, in the electrophoresis experiment, the iron hydroxide colloidal particles move toward the cathode, and the arsenic trisulfide colloidal particles move toward the anode. Electrophoresis can be used to separate sols with different charges.

For example, the clay used in the ceramic industry often contains iron oxide. To remove iron oxide, the clay and water can be stirred together to form a suspension. Since the clay particles are negatively charged, the iron oxide particles are positively charged and are energized and near the anode. Will gather very pure clay. Electrophoresis is also used in factory dust removal. Electrophoresis can also detect isolated substances, playing an important role in biochemical and clinical diagnosis. In the late 1940s and early 1950s, electrophoresis using support materials such as filter paper electrophoresis, cellulose acetate membrane electrophoresis, and agar electrophoresis was carried out. In the late 1950s, starch gel electrophoresis and polyacrylamide gel electrophoresis appeared.

Application field

Electrophoresis has been increasingly used in various fields such as analytical chemistry, biochemistry, clinical chemistry, toxicology, pharmacology, immunology, microbiology, and food chemistry. In a direct current electric field, the phenomenon that charged particles move toward oppositely signed electrodes is called electropho-resis. In 1807, electrophoresis was first discovered by Ferdinand Frederic Reuss of the Moscow University in Russia, but it was not until 1937 that Tiselius of Sweden established boundary electrophoresis for protein separation. The electrophoresis technology began to be applied. In the 1960s and 1970s, electrophoresis technology developed rapidly when media such as filter paper and polyacrylamide gel were introduced into the electrophoresis. The colorful electrophoresis format makes it widely used. In addition to the separation and analysis of small molecular substances, electrophoresis technology is mainly used for the study of proteins, nucleic acids, enzymes, and even viruses and cells. Because some electrophoresis devices are simple, easy to operate, and have high resolution and selectivity, they have become commonly used in medical testing.

Electrophoresis, also known as electrophoresis, swimming paint, electrodeposition. Founded in the 1960s, Ford Motor Company was first used in automotive primers. Due to its excellent anti-corrosion and anti-rust functions, it has been widely used in the military industry. In recent years, it has been applied to the surface treatment of daily-use hardware. Due to its excellent quality and high environmental protection, it is gradually replacing traditional paint spraying.

Electrophoretic paint film

The electrophoretic paint film has the advantages of fullness, uniformity, smoothness and smoothness of the coating, hardness and adhesion of the electrophoretic paint film,

Corrosion resistance, impact performance and permeability are significantly better than other coating processes.

Detailed features:

(1) Using water-soluble paint, using water as the dissolution medium, saving a lot of organic solvents, greatly reducing air pollution and environmental hazards, safety and hygiene, while avoiding fire hazards;

(2) high coating efficiency, small coating loss, and the utilization rate of paint can reach 90%~95%;

(3) The coating film has uniform thickness, strong adhesion, good coating quality, and uniform and smooth paint film can be obtained in various parts of the workpiece such as inner layer, depression, weld seam, etc., and other coating methods are solved for complex shape workpieces. Painting problem

(4) High production efficiency, automatic continuous production can be realized in construction, and labor efficiency is greatly improved;

(5) The equipment is complex, the investment cost is high, the power consumption is large, the temperature required for drying and curing is high, the management of coating and painting is complicated, the construction conditions are strict, and wastewater treatment is required;

(6) Only water-soluble paints can be used. The color cannot be changed during the painting process, and the stability of the paint storage is not easy to control.

(7) Electrophoresis coating equipment is complex and has high technology content, which is suitable for fixed color production.

Electrophoresis type

1. Mobile interface electrophoresis: a mixture of ions (such as anions) to be separated is placed at one end of the electrophoresis tank (such as a negative electrode), and the sample has a clear interface with the carrier electrolyte before the start of electrophoresis. After the start of electrophoresis, the charged particles move to the other pole (positive electrode), and the ions with the fastest swimming speed are at the forefront, and other ions are arranged in order of the speed of the electrodes to form different zones. Only the interface of the first zone is clear, achieving complete separation, which contains the ions with the fastest electrophoresis speed, and most of the other zones overlap.

2. Zone electrophoresis: on a certain support, in a uniform carrier electrolyte, the sample is added to the middle position. Under the action of the electric field, the ions with positive or negative charge in the sample are respectively at different speeds to the negative or positive electrode. Move and separate into zones that are separated from one another. Zone electrophoresis can be divided into paper and other fiber membrane electrophoresis, powder electrophoresis, gel electrophoresis and silk electrophoresis according to the physical properties of the support.

3. Isoelectric focusing electrophoresis: the ampholyte is added to the electrophoresis tank containing the pH gradient buffer, and when it is in an environment lower than its own isoelectric point, it is positively charged and moves to the negative electrode; if it is at In an environment above its own isoelectric point, it negatively moves to the positive pole. When swimming to its own unique isoelectric point, its net charge is zero, the swimming speed drops to zero, and substances with different isoelectric points are finally focused on their respective isoelectric points to form a clear zone. The resolution is extremely high.

4. Isotachophoresis: The sample is spiked with leading ions (the mobility is larger than all separated ions) and the terminal ions (the mobility is smaller than all separated ions), the sample is added to the leading ion and the final Between the last ions, under the action of the external electric field, each ion moves, and after a period of electrophoresis, complete separation is achieved. The zones of the separated ions are sequentially arranged in the size of the mobility between the zone of the leading ion and the terminal ion. Since no suitable supporting electrolyte is used to carry the current, the resulting zones are interconnected (Fig. d), and the interface is clear due to the "self-correcting" effect, which is different from zone electrophoresis.

Fundamental

Biomacromolecules such as proteins, nucleic acids, polysaccharides, etc. mostly have cationic and anionic groups called zwitterions. Particles are often dispersed in solution, and their electrostatic charge depends on the H+ concentration of the medium or interaction with other macromolecules. In an electric field, charged particles migrate toward the cathode or anode, and the direction of migration depends on their charged symbols. This migration phenomenon is called electrophoresis.

If the colloidal solution of the biomacromolecule is placed in an undisturbed electric field, the driving force for the particle to have a constant migration rate is derived from the effective charge Q and the potential gradient E on the particle. They compete with the frictional resistance f of the medium. This counterbalance in the free solution obeys Stokes' law.

F=6πrvη

Here v is the moving speed of the particles having a radius r in the medium viscosity η. But in the gel, this counterbalance does not fully comply with Stokes' law. F depends on other factors in the medium, such as gel thickness, particle size, and even infiltration of the medium.

The electrophoretic mobility (mbility) m is defined as the migration distance d of the particles in time t under the influence of the potential gradient E.

d

m= ------------ or m=V / E

t·E

The difference in mobility provides the basis for separating the material from the mixture, and the migration distance is proportional to the mobility.

Electrophoresis classification

The electrophoresis methods currently used can be roughly divided into three categories: microelectrophoresis, free-interface electrophoresis and zone electrophoresis. Zone-band electrophoresis is widely used, and zone electrophoresis can be divided into the following types:

According to the physical properties of the support, zone electrophoresis can be divided into:

(1) paper paper is a support for paper electrophoresis;

(2) powder electrophoresis: such as cellulose powder, starch, glass powder electrophoresis;

(3) Gel electrophoresis: such as agar, agarose, silica gel, starch gel, polyacrylamide gel electrophoresis;

(4) Edge electrophoresis: such as nylon filament, rayon electrophoresis

2. According to the form of the device of the support, the zone electrophoresis can be divided into:

(1) Plate electrophoresis: The horizontal placement of the support is the most commonly used electrophoresis method;

(2) Vertical plate electrophoresis: Polyacrylamide gel can be made into vertical plate electrophoresis.

(3) Columnar (tubular) electrophoresis: Polyacrylamide gel can be poured into a suitable electrophoresis tube to make a tubular electrophoresis.

3. According to the continuity of pH, zone electrophoresis can be divided into:

(1) continuous pH electrophoresis: such as paper electrophoresis, cellulose acetate membrane electrophoresis;

(2) Non-continuous pH electrophoresis: such as polyacrylamide gel disk electrophoresis.

Application

1. Polyacrylamide gel electrophoresis can be used to identify the purity of protein. Polyacrylamide gel electrophoresis has both charge effect and molecular sieve effect, which can separate substances with the same molecular size and different amounts of charge, and can also have the same band. Separate substances of quantitative charge and different molecular sizes. The resolution is much higher than the general chromatographic method and electrophoresis method, and the sample of 10-9~10-12g can be detected, and the repeatability is good, and there is no electroosmotic effect.

2. SDS polyacrylamide gel electrophoresis can determine the molecular weight of protein. The principle is that a large amount of charged SDS binds to the protein molecule to overcome the influence of the original charge of the protein molecule to obtain a constant charge / mass ratio. SDS polyacrylamide gel electrophoresis has been successful in measuring the molecular weight of proteins. This method has a short measurement time and high resolution. The required sample volume is very small (1~100μg), but it is only suitable for spherical or substantially spherical proteins. Some proteins are not easily combined with SDS such as papain, ribonuclease, etc., and the results are inaccurate.

3. Polyacrylamide gel electrophoresis can be used for protein quantification. The gel after electrophoresis is scanned by a gel scanner to give quantitative results. The gel scanner is mainly used for scanning the zone after one-dimensional electrophoresis of the sample and the spot after two-dimensional electrophoresis.

4. Agar or agarose gel immunoelectrophoresis can be used to 1) check the purity of the protein preparation; 2) analyze the components of the protein mixture; 3) study whether the antiserum preparation has antibodies against a known antigen; 4) test Whether the two antigens are the same.