Gas Chromatography is a technique that take a mixture of gasses and separates it out into the individual gasses.
There are lots of reasons to perform gas chromatography. The most basic is so that one can determine what gasses are present in a sample. In mass spectrometry, gas chromatography is used to separate the gas we want to analyze from other contaminant gasses.
For example, most of the time we analyze carbon dioxide, which we generate from samples in numerous ways. These methods often cause nitrogen gas and water vapor to enter the system with the carbon dioxide. Through gas chromatography, we can see separate peaks for carbon dioxide, nitrogen, and water.
A common way to do this is using a ‘column’, which is a small tube packed with special materials that will slow down specific gasses. Some columns are only a few inches long. Others are actually ten meter long coils of tiny tubes. By altering the gas flow and the temperature of the column, we can control how quickly gasses pass through the column and how far apart the different gas peaks are.