In chromatography, the mobile phase can be gas or liquid, which can be divided into gas chromatography (GC) and liquid chromatography (LC). The stationary phase can be either a solid or a liquid coated on a solid. Therefore, gas chromatography and liquid chromatography can be divided into gas-liquid chromatography, gas-solid chromatography, liquid-solid chromatography, and liquid-liquid chromatography. Chromatography.
 
In addition, there is a kind of supercritical fluid chromatography (supercritical fluid chromatography SFC). Supercritical fluid chromatography uses supercritical fluid as the circulating phase, solid adsorbent (such as silica gel) or bonded to the carrier (or capillary wall). The polymer is a stationary phase chromatography.
 
Supercritical fluid is a state of matter above the critical pressure and critical temperature. It is neither a gas nor a liquid, but has certain properties of both gas and liquid (Ding Li, Editor-in-Chief of Pharmaceutical Chromatography, People's Medical Publishing House, 2008 July first edition).
 
High Performance Liquid Chromatography (HPLC) is a new chromatographic technology that uses liquid as the mobile phase developed in the early 1970s after gas chromatography.
 
High performance liquid chromatography is developed on the basis of gas chromatography and classical chromatography. There is no essential difference between modern liquid chromatography and classic liquid chromatography. The only difference is that modern liquid chromatography is more efficient and automated than classic liquid chromatography.
 
Classic liquid chromatography, the mobile phase is transported under normal pressure, the stationary phase used has low column efficiency and long analysis cycle. However, modern liquid chromatography quotes the theory of gas chromatography, and the mobile phase is changed to high pressure delivery (high delivery pressure can reach 4.9´107Pa);
 
The chromatographic column is packed with small particle size fillers in a special method, so that the column efficiency is much higher than that of classic liquid chromatography (the number of plates per meter can reach tens of thousands or hundreds of thousands);
 
At the same time, a high-sensitivity detector is connected after the column, which can continuously detect the effluent. Therefore, high performance liquid chromatography has the characteristics of fast analysis speed, high separation efficiency, and automation. So people call it high-pressure, high-speed, high-efficiency or modern liquid chromatography.
 
HPLC system is generally composed of high performance liquid chromatograph, mainly composed of sampling system, infusion system, separation system, detection system and data processing system.
 
The high-pressure infusion pump, chromatographic column and detector are the key components. Some instruments include gradient elution device, online degasser, autosampler, pre-column or guard column, column temperature controller, etc. Modern HPLC instruments also have a microcomputer control system for automatic instrument control and data processing. The preparative HPLC instrument is also equipped with an automatic fraction collection device.