Gas chromatography (GC)

Gas Chromatography (GC) is an analytical tool used to identify and quantitate a wide variety of compounds in a mixture. GC utilizes a compound’s intrinsic affinity for a “stationary phase” (solid support with specialized coating) and facilitates the separation of complex sample matrices into their component parts.

Essentially in gas chromatography, a sample is injected into the hot inlet of a gas chromatogram, which volatilizes the components in the sample. Next, an inert gas (“carrier gas”) carries the volatile compounds through a coated capillary column. The capillary coating or “stationary phase” is housed inside the capillary column. The flame ionization detector (FID) passes sample and “carrier gas” from the column through a hydrogen-air flame. The hydrogen-air flame alone creates few ions, but when an organic compound is burned there is an increase in ions produced. A polarizing voltage attracts these ions to a collector located near the flame. The current produced is proportional to the amount of sample being burned. This current is sensed by an electrometer, converted to digital form, and sent to a data system where a chromatogram is electronically constructed. The time it takes a specific compound to pass through the capillary column and to a detector is called its “retention time.” Retention time, which is inherently related to a compounds affinity to the stationary phase, can be used to identify the compound in question when compared to a reference standard.