Separation and Purification of protein

　　Separation and purification of protein;from small molecules Looking at the development prospects, the future will always bring positive effects. https://www.all-chemistry.com/

　　1. Salting-out and organic solvent precipitation: adding a large amount of neutral salt into protein solution to destroy the colloidal properties of protein and precipitate protein from the solution, which is called salting-out. Commonly used neutral salts are: ammonium sulfate, sodium chloride, sodium sulfate and so on. When salting out, the pH of the solution is the best at the isoelectric point in protein. Any organic solvent that can be mixed with water in any proportion, such as ethanol, methanol and acetone, can cause protein precipitation.

　　2. Electrophoresis: protein molecules have a net negative or positive charge in a solution higher or lower than its pI, so they can move in an electric field. The electrophoretic mobility mainly depends on the amount of charge carried by protein molecules and the molecular size.

　　3. Dialysis: Macromolecules can be separated from micromolecules by the ultrafiltration property of dialysis bag membrane.

　　4. Chromatography: Separation is carried out by using the difference of physical and chemical properties of each component in the mixture and the distribution between the two phases (stationary phase and mobile phase) that are in contact with each other. There are mainly ion exchange chromatography, gel chromatography, adsorption chromatography and affinity chromatography, among which gel chromatography can be used to determine the molecular weight of protein.

　　5. Ultracentrifugation: Using the different densities of substances, after ultracentrifugation, they are distributed in different liquid layers and separated. Ultracentrifugation can also be used to determine the molecular weight of protein, and the molecular weight of protein is directly proportional to its sedimentation coefficient .