Chromatographic analysis is one of the active branches of analytical chemistry and an important means of material separation analysis. It is increasingly used in environmental, biochemical, and fine chemical product analysis. Application of chromatography related technologies is involved in almost all fields. From classical plate chromatography to column chromatography, from gas chromatography, liquid chromatography, supercritical fluid chromatography to capillary electrophoresis and electrochromatography, it plays an important role in scientific research and industrial production.
- Originof chromatographic technology
The ancient Romans used a piece of cloth or a piece of paper to analyze dyes and pigments. More than 100 years ago, German chemists improved the method to make it more reproducible and quantitative, which later became today's paper chromatography technology. In 1901, Russian botanists used calcium carbonate as an adsorbent to separate plant pigments. Then in 1903, a new method for separating plant pigments by adsorption principle was proposed. In 1906, this method was officially named as chromatography, but it was not taken seriously due to the slow and inefficient separation. Until 1931, German scientists used a similar method to separate more than 60 kinds of pigments such as carotene, and chromatographic methods were then widely used.
- Development and application of gas chromatography technology
Since the first creation of practical gas-liquid chromatography in the world in 1952, gas chromatographs, as a representative of modern analytical instruments, have developed into an industry with considerable production scale and formed a discipline with considerable knowledge of detection technology. Gas chromatography is widely used in environmental samples for pollutant analysis, drug quality testing, natural product composition analysis, pesticide residue determination in food and industrial products, quality control and other fields due to its high separation efficiency, fast analysis speed and good selectivity. With the advent of new gas chromatography instruments, detectors, and data analysis methods, the application fields of gas chromatography will become more and more extensive.
The combination of gas chromatography and other technologies has also developed very rapidly in recent years. It is mainly used in combination with mass spectrometry, spectroscopy, etc., combined with chemical reactions, and computer. Gas chromatography is an effective tool for separating complex mixtures, but it is not possible to qualitatively identify unknowns; mass spectrometry, spectroscopy, and nuclear magnetics are effective tools for identifying unknown structures, but require that the samples analyzed be as simple as possible, not complex mixtures. The combination of chromatography and these techniques is therefore a recognized and effective tool for dissecting the structure of unknowns in complex mixtures. In recent years, the development of the two technologies is directly combined, eliminating the need to collect condensation in the middle, so that the analysis time is shortened and the sample consumption is reduced.
Organic mass spectrometers, magnetic mass spectrometry, quadrupole mass spectrometry, ion trap mass spectrometry, time-of-flight mass spectrometry (T0F), and Fourier transform mass spectrometry (FTMS) are currently available on the market to be combined with gas chromatography. With the continuous updating of interface technology, the interface devices are smaller and simpler, and the shape is lighter. The function of GC-MS is more powerful. The resolution of GC-TOFMS can reach about 50M. The combination of GC-MS plays an important role in many areas of analytical testing and scientific research, especially as a necessary tool in the routine testing of many organic compounds. It is widely used in environmental protection, health, food, agriculture, petroleum, chemical and other industries.
- Development and application of liquid chromatography
At the beginning of liquid chromatography, a large diameter glass column is used to transport the mobile phase with a liquid level difference at room temperature and pressure, called classical liquid chromatography. Liquid chromatography is a type of separation and analysis technique characterized by a liquid as a mobile phase. The stationary phase can take many forms, such as paper, sheets, and packed beds. The mobile phase of classical liquid chromatography relies on gravity to flow slowly through the column, so the particle size of the stationary phase cannot be too small. The separated samples are collected after classification and analyzed, so that the classical liquid chromatography not only has low separation efficiency, slow analysis speed, but also complicated operation. It was not until the 1960s that a stationary phase with a particle size of less than 10 μm was developed, and a high-pressure infusion pump and an automatically recorded detector were used to overcome the shortcomings of classical liquid chromatography and to develop into liquid chromatography.
Liquid chromatography (LC) is a widely used field in various chromatographic modes. About 80% of the compounds in the world are analyzed by different modes of HPLC (such as normal phase HPLC, reverse phase HPLC, ion exchange chromatography and ion chromatography, volume exclusion chromatography, affinity chromatography, etc.) , including high molecular compounds, ionic compounds, heat labile compounds and biologically active compounds.
Liquid chromatography is developed from gas chromatography and liquid chromatography, and its structure and operation process are perfect. New research and development of liquid chromatography and its combined technologies have been widely used in chemical production, pharmaceutical industry, food industry, biochemical, medical clinical testing and environmental monitoring. Compared with the chromatography method, many other detection methods are ultimately not as stable, reliable and eliminated as liquid chromatography after long-term repeated verification, their feasibility, accuracy, precision and efficiency. It can be seen that liquid chromatography is not only of extraordinary significance to the present, but also has considerable development prospects in the near future.
- Development and application of supercritical fluid chromatography
Supercritical fluid chromatography (SFC) is a chromatographic method in which a supercritical fluid is used as a mobile phase. Supercritical fluids are substances that are neither gases nor liquids. Their physical properties are between gas and liquid. Supercritical fluid chromatography is a new chromatographic technique developed in the 1980s. It has advantages not found in the gas phase and liquid phase, and it can separate and analyze some objects that cannot be solved by gas and liquid chromatography. The application is very extensive and the development is very rapid. According to industry estimates, about 25% of all separations have involved difficult-to-handle substances, and supercritical fluid chromatography can achieve satisfactory results.
Supercritical fluids have physical properties that are extremely advantageous for separation, which are just between the gas and the liquid. The diffusion coefficient and viscosity of the supercritical fluid are close to that of gas chromatography, so the mass transfer resistance of the solute is small, and rapid separation can be obtained. On the other hand, its density is similar to that of liquid chromatography, which facilitates the separation and analysis of substances with high thermal instability relative to molecular mass at lower temperatures. In addition, the physical and chemical properties of supercritical fluids, such as diffusion, viscosity, and solvent forces, are functions of density. Therefore, as long as the density of the fluid is changed, the properties of the fluid can be changed, and it is not necessary to pass the gas-liquid equilibrium curve from a similar gas to a similar liquid. Supercritical fluid chromatography is widely used in environmental protection, medicine, food and agriculture.
- Development and application of capillary electrochromatography
Capillary electrochromatography (CEC) is a new separation technique developed on the basis of capillary electrophoresis and microcolumn liquid chromatography. Due to technical limitations, until the 1990s, the research of capillary electrochromatography was rapidly developed.
At present, capillary electrochromatography is the leader tool in drug analysis, focusing on the separation of drug-related impurities and the separation of chiral drugs. The analysis targets mainly neutral drugs and polycyclic aromatic compounds. With the continuous improvement and improvement of capillary electrochromatography technology, it will be applied in the analysis of biotechnology, environmental protection, agricultural chemistry, fine chemical products, food industry and other fields. According to the current development trend of capillary electrochromatography technology, CEC as a developing separation technology will have wider application prospects in the foreseeable future.
Since the establishment of chromatography, whether it is the development and improvement of basic theory of chromatography, new separation mode, new stationary phase equipment, chromatography or capillary electrophoresis instruments, it has been rapidly developed in its practical application. In terms of column type, classical columns are currently commonly used. The capillary column is very suitable for trace analysis and has fast analysis speed and low sample consumption, which is one of the future development directions of the column type. It is foreseeable that future chromatographic technologies will be developed in conjunction with other technologies, to high precision, high sensitivity and miniaturization.
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