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Chromatography, known as chromatography analysis as well, is a type of separation and analysis method. The common chromatography methods primarily consists of column chromatography (CC), thin layer chromatography (TLC), high-performance liquid chromatography (HPLC), gas chromatography (GC) and supercritical fluid chromatography (SFC).
1. Column Chromatography (CC)
As the original chromatography, it injects the stationary phase into the glass tube with cotton or filter paper plugged at its bottom, and spread the stationary phase powder, saturated by sample, on the top of the glass tube, and use the liquid phase for elution.
There are two commonly used elution ways. One depends on the gravity of the solvent itself for elution from top to bottom, and the other utilizes the capillarity for elution from bottom to top.
There are also two different methods for recycling pure components after separation. One directly receives the solution at the end of the column, and the other utilizes the mechanical method to separate each ribbon after drying the stationary phase and extract components by soaking the stationary phase in a proper solvent. Column chromatography is widely used for separating mixtures, including organic synthetic products, natural extracts and biological macromoleculars.
2. Thin Layer Chromatography (TLC)
Thin layer chromatography has quite extensive applications. Spread the stationary phase on the metal or glass sheet to form a thin layer, and point the sample to one end of the sheet with a capillary tube, pen or other tool, and then immerse this end into the mobile phase. The capillary action can make the mobile phase flow up the sheet to unroll the sample. It is mainly used for rough test of samples and test of organic synthesis reaction process.
3. High-Performance Liquid Chromatography (HPLC)
High-performance liquid chromatography is one of the most commonly used chromatography methods. The system is composed of mobile phase storage flask, infusion pump, sample injector, chromatography column, detector and recorder. It is similar to gas chromatography, but make many adjustments due to its mobile phase is liquid. The infusion pump in HPLC should have a stable and balanced infusion volume, and the sample injector should be convenient to load sample and strict to switch. HPLC is widely used in various fields of quantitative and qualitative analysis.
4. Gas Chromatography (GC)
Gas chromatography is a kind of separation method that uses helium, argon or other gas as the mobile phase and adds the sample into the chromatography column containing the stationary phase. After separation, ach component is changed into electrical signal by detector and is recorded by recorder. Gas chromatography has developed rapidly over the last twenty years. Although it has various types, it is generally composed of five parts, including gas source, sampling system, chromatography column, detector and recorder. The chromatography is the heart of the chromatography.
5. Supercritical Fluid Chromatography (SFC)
Supercritical fluid chromatography is a kind of chromatography process that takes supercritical fluid as the mobile phase and depends on its solvability for separation and analysis. It is a kind of new technology developed and improved in the 1980s.
Supercritical fluid chromatography combines the characteristics of both gas chromatography and liquid chromatography. Not only can it analyse samples with high boiling point and low volatility that gas chromatography isn’t suitable for, but it has quicker analysis speed and condition compared to high-performance liquid chromatography. The operating temperature mainly depends on the fluid selected. The commonly used fluids are carbon dioxide and nitrous oxide. The supercritical fluid is easy to control and regulate, which can turn into gas, liquid or keep the state of supercritical fluid before entering the detector. As a result, it can connect to any liquid or gas phase detector, and can match with various types of detectors, expanding its application scope and classification ability and having a wide range of choice in qualitative and quantitative aspects. It can also use various gradient technologies to optimize the chromatography condition and can easily reach a higher column efficiency compared to high-performance liquid chromatography.
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