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Purge and Trap Gas Chromatography

Gas Chromatography (GC) is the process of analyzing compounds using a gas chromatograph-a machine that analyzes compounds after they are separated from the sample and vaporized. A column inlet (a.k.a. injector) removes the compounds from the sample, vaporizes them, and injects them into the column of the chromatograph. For purge and trap gas chromatography, which is typically performed to analyze compounds that occur at low parts per billion (ppb) levels, a purge and trap column inlet is used.

Purgingand Trapping

After the sample is transported to the column inlet, either manually or by an autosampler, it undergoes the following purging and trapping process before it is injected into the column of the chromatograph:

Inert gas is bubbled through the sample to release the compounds
The compounds are “trapped” on an absorbent material in the concentrator
The concentrator is heated until the compounds vaporize

After the compounds vaporize, they are transported to the column on a stream of carrier gas-a process known as the mobile phase of GC. This action concludes the purge and trap process and commences the chromatography process, which occurs as follows:

The compounds enter the column and pass through a liquid (stationary phase)
The compounds exit the column and enter the analyzer
The compounds are detected and identified by the analyzer

In laboratories, this process is typically initiated by an autosampler that moves the sample to the column inlet; in years past, samples were introduced manually. When the process is finished, the results are stored in a database and/or printed.

Common Applications

The most popular application for purge and trap gas chromatography is the analysis of Volatile Organic Compounds (VOCs), naturally occurring substances that can cause adverse health conditions and damage to the environment. In addition to being toxic to humans and animals even in small amounts, VOCs are dangerous for their tendency to vaporize at room temperature-a trait that allows them to pervade work environments and the natural environment with ease. Different products and environments have different VOC regulations, some of which are enforced by the Environmental Protection Agency (EPA), but ensuring that VOCs remain absent or within the proper limit is always accomplished with the help of GC.

VOC analysis is the best-known application for GC, but it is not the only application. GC is also used to analyze compounds that affect the taste and smell of various foods and beverages, and numerous cosmetic products and fragrances.