An overview of Gas Chromatography

Posted by Quadrex Corp on February 17th, 2020

Chromatography is a technique of separation that is used to separate different components of a mixture based on their relative solubility in a particular solvent.

Definitions

Gas chromatography is a particular type of chromatography in which the mobile phase is always gas. A gas chromatograph is used to perform this process, and it displays the acquired data in the form of a graph known as a gas chromatogram.

There are mainly two types of gas chromatography:

1. Gas-Liquid Chromatography: It is the type of gas chromatography in which the stationary phase is liquid.
2. Gas-Solid Chromatography: It is the type of gas chromatography in which the stationary phase is solid.

Gas chromatography is a powerful tool for separating analyzing the components of volatile mixtures that can vaporize to exist in a gaseous state without thermal decomposition. GLC is the most common type of gas chromatography. The steps and process of GLC are explained below:

Process- Gas-Liquid Chromatography

1. Injection : A liquid sample, called analyte, is procured or prepared. A small quantity of this sample is injected into the gas chromatograph using a small syringe at the injection port. This sample is then vaporized into the gas phase. An inert carrier gas keeps flowing through the chromatograph so that the particles of the sample mix with the carrier gas without reacting with it. This carrier gas is referred to as the mobile phase because its particles are in motion. Helium is most commonly used for this purpose. The mixture is carried into the column with the carrier gas. 

2. Column: The column is a long thin tube packed with a porous rock diatomaceous earth, which is coated with a liquid that has a high boiling point.  The coating on the GC column is called the stationary phase. A detector is placed at the end of the column. The column is present within a temperature-controlled oven that does not allow any transfer of heat.

a) The carrier gas moves along the tube more quickly and hits the detector fast. So, usually, the first peak on the chromatogram represents the carrier gas, and the second peak is the solvent of the liquid sample.

b) The peaks of the components appear in an order based on their affinity to the mobile phase. The one with the highest solubility appears first, and the one with the least solubility appears last. This is because the components with a higher solubility spend more time in the solvent, whereas the less soluble components leave the solvent fast and move towards the detector with the carrier gas.

c) The temperature of the column oven is less than the temperature of the injection oven. So, if the boiling point of a particular component is higher than the temperature in the tube, it can condense on the tube surface. But it eventually moves towards the detector as it evaporates due to prolonged heat exposure.

3. Detector: The detector identifies the different components of the mixture as they hit it. It displays the results in the form of a chromatogram. The x-axis represents the time taken by a particular component to reach the detector, and the y-axis represents the amount of the component present.

Conclusion

In case you run an industry or a science laboratory, a gas chromatograph can be used for various purposes ranging from determining vapor pressure to detecting any contamination. A GC column supplier can assist you in finding a good quality gas chromatograph that provides reliable and accurate results.