Gas chromatography is a novel technique for separating and quantitating vaporized compounds using an inert carrier gas. It operates on similar principles to column permeation chromatography, where a sample is dissolved in a mobile phase and passed through a porous stationary structure.

Compounds are characterized and quantified by the time it takes for them to elute from the permeable column. This factor is determined by multiple characteristics, including molecular weight, hydrodynamic behavior, and concentration in the mobile phase.

The differentiating factor between gas chromatography and standard chromatographic methods is the use of a vapor rather than a fluid as a mobile phase, and a liquid as opposed to a solid for the stationary phase.

How Does Gas Chromatography Work?

Non-reactive gases such as helium (He) or hydrogen (H) are used as a carrier for vaporized molecules of interest. This gaseous mixture is flowed through the column of a gas chromatograph, which comprises a microscopic fluidic membrane and an inert, solid substrate. This column partitions vapors based on their mechanical properties and their affinity with the stationary fluid. The flow-through rates of the sample’s constituent parts can be used for compound detection, identification, quantitation, and purification.

Elution in gas chromatography is electronically monitored using a detector at the outlet stream of the permeable column. This measures the retention time (tR) of compounds to qualitatively determine their adsorption characteristics with packing media of distinct chemical compositions.

Tips for Gas Chromatography

Cleanliness is a critical requirement of capillary GC as contanimination is the largest source of capillary GC problems. To avoid contamination you can take some simple steps:

Check your inlet

The inlet is the most common location for contamination so it's important that you check it regularly. A thorough inspection should include checking below the septum, in the glass liner and at the bottom of the inlet.

Keep your detector clean

If you see an increase in noise or noise spikes, or a drop in sensitivity, this could indicate that your detector needs to be cleaned. If this is the case you should check your instrument manual for instructions.

Use High Purity Gases

Your capillary GC carrier gas, typically hydrogen, nitrogen or helium, should be high purity. It's important for the carrier gas to be free of O2 and H2O as these can contaminate the detector or degrade the stationary phase.