Gas chromatography is an analysis method that has received very good theoretical development. It was a careful study of its theoretical and practical foundations that contributed to the rapid development of this technique in recent decades.
It is known that gas chromatography differs from other similar methods in that it uses gas as a mobile phase. The stationary phase may be a solid or liquid. Depending on this, one speaks of gas adsorption or gas-liquid chromatography.
The separation of mixtures of substances in devices such as a gas chromatograph occurs due to the repeated repetition of the process of distribution of components between a stationary liquid or solid phase and a moving gas. The separation process is based on the difference in volatility and solubility of the analytes. The component whose volatility at a given temperature is greater and the solubility of the stationary phase is less will move through the column faster.
The use of gas as a mobile carrier allows one to obtain advantages such as clarity of separation of constituent substances and speed of analysis. The test sample is introduced into the column in gaseous form or in the form of steam. Using this method, it is possible to analyze not only gases, but also liquid and solid substances, which are transferred to the required state by heating. In this regard, in gas chromatography, the temperature at which the whole process takes place plays a very important role. The performance limits for the gas-adsorption method of analysis range from 70 to 600 ° C, and for gas-liquid analysis from 20 to 400 ° C. The industry produces a gas chromatograph, which allows you to pre-program the temperature.
This method makes it possible to analyze substances whose molecular weight is less than 400. They do not decompose upon evaporation, and upon subsequent condensation they do not change their composition.
Mainly in analytical practice, gas-liquid chromatography is used. Compared to gas adsorption, it has some advantages, which are associated mainly with a wide selection of possible stationary liquid phases, as well as with high purity and, importantly, with the homogeneity of liquids.
Gas chromatography is an express method characterized by high accuracy, sensitivity and automation. The versatility and flexibility of this method determines the device used in a particular case. Gas chromatography, used for quantitative analysis, gives unambiguous results that are not in doubt.
This method allows you to solve many analytical problems, to separate and determine the ratio of compounds with a minimum difference in vapor pressure. The method of gas chromatography is used to purify chemicals, splitting mixtures into individual components. It is especially effective in the separation of substances of similar composition that belong to the same class: organic acids, alcohols, hydrocarbons.