Gas chromatography. Features of the method

Gas chromatography is a method of analysis that has received very good theoretical development. It is precisely the careful elaboration of his theoretical and practical foundations that has contributed to the rapid development of this methodology in recent decades.

It is known that gas chromatography differs from other similar methods in that it uses gas as the mobile phase. The stationary phase can 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 is due to a multiple repetition of the distribution of components between a stationary liquid or solid phase and a moving gas phase. The separation process is based on the difference in the volatility and solubility of the substances to be analyzed. The component, whose volatility is greater at a given temperature, and the solubility of the stationary phase is smaller, will move through the column faster.

The use of gas as a mobile carrier makes it possible to obtain such advantages as the clarity of the separation of constituent substances and the speed of the analysis. The test sample is introduced into the column in a gaseous or vapor form. With the help of this method, it is possible to analyze not only gases, but also liquid and solid substances, which are converted into a necessary state by heating. In this connection, in gas chromatography, the temperature at which the whole process takes place plays a very important role. Limits of operating parameters 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 on evaporation, but do not change their composition during subsequent condensation.

Basically, in analytical practice, gas-liquid chromatography is used. Compared with gas adsorption, it has some advantages, which are associated mainly with a wide range of possible stationary liquid phases, as well as with high purity and, importantly enough, with the uniformity of liquids.

Gas chromatography is an express method, characterized by high accuracy, sensitivity and the possibility of automation. Versatility and flexibility of this method determines the device used in this or that case. Gas chromatography, used for quantitative analysis, gives unambiguous results that are beyond doubt.

This method allows solving many analytical problems, separating and determining the ratio of compounds with the minimum difference in vapor pressure. The method of gas chromatography is used for cleaning chemical preparations, splitting mixtures into separate components. It is especially effective in the separation of substances that are similar in composition, which belong to the same class: organic acids, alcohols, hydrocarbons.