GC mainly uses differences in boiling point, polarity and adsorbability of substances to separate mixtures. The process is shown in FIG. 1 gas phase analysis flow chart.
Actually, chromatography was first discovered by the Russian botanist M.S.Tswett in 1901. In March 1903, M.S.Tswett formally proposed the word “chromatography” in his report at an academic conference at the University of Warsaw, marking the birth of chromatography. Therefore, he was nominated as candidate for the Nobel Prize in chemistry in 1917. Gas chromatography appeared in the 1940s. At that time, Tswett was studying the separation technology of liquid chromatography (LC). In the process of studying the theory of distribution chromatography, British people A.J.P. Martin and R.L.M. Synge confirmed the possibility of gas as chromatography flowing and predicted the birth of GC. Coincidentally, the two scientists awarded Nobel Prize for Chemistry. Although the achievement represented their contribution to distributive chromatography theory, some descendants believed that they got the prize because of GC technology. From another aspect, this shows the importance of GC technology to the development of the whole chemistry.
Although GC appeared 50 years later than LC, its development in the following 20 years was far behind LC. From the introduction of the first commodity GC instrument in 1955, to the advent of capillary GC column in 1958; from the study of capillary GC theory to the application of various detection technologies, GC quickly changed from a laboratory research technology to a conventional analysis method, and almost formed a dominant situation of GC in the field of chromatography. Since 1970, the development of electronic technology, especially computer technology, has made GC chromatographic technique more powerful, and the emergence of elastic quartz capillary column in 1979 has made GC on a new stage. These are not only the results of high-tech development, but also the requirements of modern industrial and agricultural production. On the other hand, chromatography greatly promoted the evolution of modern material civilization, which plays a crucial role in all aspects of modern society. From space shuttles in the sky, to aircraft carriers in the water, GC is used to monitor the quality of gas in the cabin; from food and cosmetics in daily life, to various chemical production process control and product quality inspection; from material identification in judicial inspection, to oil and gas field search in geological exploration; from disease diagnosis, medical analysis, to archaeological excavation and environmental protection, GC technology is widely used.
Gas Chromatograph is composed of the following five systems: air circuit system, sample inlet system, separating system, temperature control system, detection and recording system. Whether the components can be separated depends on the chromatographic column, and can be identified after separation depends on the detector, so the separation system and detection system are the core of the instrument.
After vaporization in the vaporization chamber, the sample to be analyzed is carried into the column by inert gas (carrier gas, also known as mobile phase). The column contains liquid or solid stationary phase. Due to different boiling points, polarity or adsorption properties, each component tends to form a distributive or adsorption equilibrium between the mobile phase and stationary phase. However, because carrier gas is mobile, this balance is actually difficult to establish. It is also due to the carrier gas flow, so that the sample components in the movement of repeated distribution or adsorption or desorption. The result is that the higher concentration components in carrier gas flow out of the column first, while in the fixed phase, the larger concentration of distribution is distributed out later. As the components leave the column, they enter the detector immediately. The detector can convert the sample components into an electrical signal, and the size of the electrical signal is proportional to the amount or concentration of the components being measured. When these signals are amplified and recorded, they are known as gas chromatograms.
In the petrochemical industry, most raw materials and products can be analyzed by gas chromatography. In the power department, it can be used to check latent fault of transformer; In environmental protection, it can be used to monitor the quality of urban air and water; In agriculture, it can be used to detect pesticide residues in crops; In the commercial sector, it can be used to test and identify the quality of food; In medicine, it can be used to study human metabolism and physiological function; In clinical, it can be used to identify drug poisoning or disease patterns; In the space capsule, it can be used to automatically monitor the gas in the spacecraft chamber and so on.
As social economy and scientific technology develop, human civilization makes great progress. However, GC technology also caused more and more serious damage to the ecological environment. Nowadays, environmental pollution has become one of the biggest challenges faced by mankind. Countries in the world are making great efforts to control and govern various kinds of environmental pollution. For example, the US Environmental Protection Agency (EPA) and China Environmental Protection Administration have issued a number of standard analytical methods. The application of GC in environmental analysis mainly includes the following aspects:
4.2.1 Air pollution analysis (toxic and harmful gases, gas sulfides, nitrogen oxides, etc.);
4.2.2 Drinking water analysis (PAH(polycyclic aromatic hydrocarbon), pesticide residues, organic solvents, etc.);
4.2.3 Water resources (including organic pollutants in fresh water, seawater and waste water);
4.2.4 Soil analysis (organic contaminants);
4.2.5 Solid waste analysis.
4.3.1 Fatty acid methyl ester analysis;
4.3.2 Pesticide residue analysis;
4.3.3 Flavoring analysis;
4.3.4 Food additive analysis;
4.3.5 Analysis of volatiles in food packaging materials.
4.4.1 Estriol determination;
4.4.2 Determination of gestational diol and gestational triol in urine；
4.2.3 Determination of cholesterol in urine;
4.2.4 Analysis of catecholamine metabolites;
4.2.5 Analysis of alcohol, anesthetics and amino acid derivatives in blood;
4.2.6 Analysis of testosterone in the blood;
4.2.7 Analysis of certain volatile drugs.
4.5.1 Study on specific surface area and adsorption properties;
4.5.2 Solution thermodynamics;
4.5.3 Determination of vapor pressure;
4.5.4 Complexation constant specific surface area determination;
4.5.5 Reaction kinetics;
4.5.6 Measurement of virial coefficient.
4.6.1 Monosomic analysis;
4.6.2 Additive analysis;
4.6.3 Copolymer composition analysis;
4.6.4 Polymer structure characterization;
4.6.5 Analysis of impurities in polymers;
4.6.6 Thermal stability study.