Gas Chromatography in Lab Testing

mass spectrometry
Written by Cara Wietstock

Like liquid chromatography (LC), gas chromatography (GC) is a method used in analytical chemistry to separate compounds so that they can be analyzed. The process of GC takes us through a mobile phase and a stationary phase to log the retention times. This is the basic functionality behind this commonly used lab testing method.

gas chromatography

The difference from LC to GC is the mobile phase which is a vapor in GC and a liquid when using liquid chromatography. Though it is very similar to LC, HPLC, TLC, and column chromatography there are some notable differences when looking analytically at the process of GC. GC is often used to prepare pure compounds from a mixture, with cannabis it is used to isolate the various chemical compounds (cannabinoids, pesticides, etc.) in flower, extractions, and/or edibles.

About 90% of gas chromatographs use Helium, but most lab analysts prefer to use hydrogen for improved separations. Nitrogen is also used. The column comes into play after the gas in the stationary phase which turns the sample into either a liquid or polymer in a column. The gaseous compounds are analyzed by how they interact with the inside of the column that is now coated with the stationary phase liquid or polymer. Each compound will elute at a different time, this is called the retention time. Retention times are what lab analysts will compare to measure various compounds of the strain or concentrate.

gas chromatography

SRI Instruments GC Model

There are a couple of differences between GC, often called “Gas-liquid chromatography”, and the other testing methods mentioned above. Unlike column chromatography, GC the separation of compounds in a mixture happens between a liquid stationary phase and gas mobile phase. Another difference is that when using GC we can control the temperature of the column because it is enclosed in an oven. This fact leads to more accurate results that basic column chromatography. 

About the author

Cara Wietstock

Cara began working in the retail cannabis industry of San Francisco, CA in 2011 and continued in that sector for years. In 2015 she dedicated herself to writing full-time. Her passion for the written word and deep respect for the healing properties of the plant have brought her to Terpenes and Testing magazine. She now helps keep us on the cutting edge of scientific cannabis discovery as the Editor-in-Chief of the print publication.

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