What is Gas Chromatography? How gas Chromatography is done?


What is Gas Chromatography?

Gas Chromatography is the technique used for analyzing hydrocarbon mixtures. A gas chromatographer is a laboratory instrument. Gas samples are brought to the laboratory to test and put into the chromatographer to produce a chromatograph.

A Chromatographer consist functional components sample handling, the chromatographer oven and controller electronics. The analysis processing provides the component concentrations and the other calculated
values through physical reports or interfaces to other devices.

Functional diagram:

gas chromatography

The left side of the block diagram carrier gas processing.

Carrier gas:

Carrier gases are usually inert gases which don’t react with the sample gas. Commonly used inert gases are helium, argon and carbon dioxide. The carrier gas is chosen dependent on the detector used.

The carrier gas is processed split into two paths one as the reference and other is sprayed and mixed with sample gas.

Sample injector:

Commonly used injection method is the microsyringe with a rubber septum into a flash vaporizer port at the head of the column. The temperature at the sample injector is kept at 50-degree Celsius.

The sample is injected into the carrier gas and it is set to pass to the chromatograph oven.

Chromatograph oven:

The performance of the chromatographer will be affected by the temperature change. It is the oven maintain the temperature of the gas at the column at a fixed temperature. The temperature at which the oven is controlled is dependent on the gas used and the detector used in the chromatographer.

Heavier the hydrocarbon used hotter the oven should be.

Chromatography column:

This column separates the gas mixture into individual components. The “boiling point” is the technique used to separate the gases. As the gas sample moves through the column, components with lower boiling points move more slowly than the components with higher boiling points. The speed at which this separation occurs is dependent on the temperature of the column.


After the separation of the gases, gas is allowed to pass through the detectors. Both the sample gas and the reference gases are applied through the detector. The detector compares the gas properties.

Commonly used detector is thermal conductive detector shown below

<img src="/uploads/default/original/2X/8/88c014a258cf6cf0185c68963f398b24ea67ec4f.png" width=“500” height="378"alt=“gas chromatography”>

The reading is then converted to a recordable format.

A gas chromatography may look like as shown below.

gas chromatography