Definition of Chromatography
Chromatography is an effective method for separating and identifying compounds.
Application of Chromatography
- Separate the mixture. The active parts of Chinese medicine extracts often contain a mixture of several components with similar structures and similar physical and chemical properties. It is difficult to separate them by general chemical methods, and they can be separated by chromatography.
- Refined compounds. When the active ingredients are extracted and separated, they often contain a small amount of impurities with similar structures, which are not easy to remove. Chromatography can also be used to remove impurities to obtain pure products.
- Identification of compounds. Under certain conditions, pure compounds have a certain Rf value in thin-layer chromatography or paper chromatography, and have a certain retention time in gas chromatography and high-performance liquid chromatography, so the purity of the compound can be identified by chromatography or by standard The comparison of products is used to preliminarily determine whether two compounds with similar properties are the same substance.
Choice of Chromatographic Conditions
Due to the different types and properties of the active ingredients of traditional Chinese medicine, the selection of chromatographic conditions is different.
Generally, silica gel or alumina column chromatography can be used for the isolation of alkaloids, and partition chromatography can be used for alkaloids with higher polarity, and partition chromatography or ion exchange chromatography can also be used for quaternary ammonium water-soluble alkaloids.
The chromatographic isolation of glycosides often depends on the properties of aglycones, such as saponins and cardiac glycosides, which can generally be used for partition chromatography or silica gel adsorption chromatography.
Volatile oils, steroids, terpenoids, including terpenoid lactones, are often the first choice for chromatography on alumina and silica gel.
Polyamide adsorption chromatography can be used for polyphenol derivatives such as flavonoids and tannins.
For organic acids and amino acids, ion exchange chromatography can generally be used, and sometimes partition chromatography can also be used. Some amino acids can also be chromatographed by activated carbon adsorption.
For macromolecular compounds, such as peptides, proteins, and polysaccharides, gel chromatography is commonly used.
In general, alumina or silica gel adsorption chromatography is often considered for non-polar components. If the polarity is large, distribution chromatography or weak adsorbent adsorption chromatography is used. For acidic, basic, and amphoteric components, ion exchange chromatography can be used. Sometimes adsorption chromatography and partition chromatography can also be used.