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gas chromatography

n. gas-liquid chromatography

Wikipedia
Gas chromatography

Gas chromatography (GC) is a common type of chromatography used in analytical chemistry for separating and analyzing compounds that can be vaporized without decomposition. Typical uses of GC include testing the purity of a particular substance, or separating the different components of a mixture (the relative amounts of such components can also be determined). In some situations, GC may help in identifying a compound. In preparative chromatography, GC can be used to prepare pure compounds from a mixture.

In gas chromatography, the mobile phase (or "moving phase") is a carrier gas, usually an inert gas such as helium or an unreactive gas such as nitrogen. Helium remains the most commonly used carrier gas in about 90% of instruments although hydrogen is preferred for improved separations. The stationary phase is a microscopic layer of liquid or polymer on an inert solid support, inside a piece of glass or metal tubing called a column (an homage to the fractionating column used in distillation). The instrument used to perform gas chromatography is called a gas chromatograph (or "aerograph", "gas separator").

The gaseous compounds being analyzed interact with the walls of the column, which is coated with a stationary phase. This causes each compound to elute at a different time, known as the retention time of the compound. The comparison of retention times is what gives GC its analytical usefulness.

Gas chromatography is in principle similar to column chromatography (as well as other forms of chromatography, such as HPLC, TLC), but has several notable differences. First, the process of separating the compounds in a mixture is carried out between a liquid stationary phase and a gas mobile phase, whereas in column chromatography the stationary phase is a solid and the mobile phase is a liquid. (Hence the full name of the procedure is "Gas–liquid chromatography", referring to the mobile and stationary phases, respectively.) Second, the column through which the gas phase passes is located in an oven where the temperature of the gas can be controlled, whereas column chromatography (typically) has no such temperature control. Finally, the concentration of a compound in the gas phase is solely a function of the vapor pressure of the gas.

Gas chromatography is also similar to fractional distillation, since both processes separate the components of a mixture primarily based on boiling point (or vapor pressure) differences. However, fractional distillation is typically used to separate components of a mixture on a large scale, whereas GC can be used on a much smaller scale (i.e. microscale).

Gas chromatography is also sometimes known as vapor-phase chromatography (VPC), or gas–liquid partition chromatography (GLPC). These alternative names, as well as their respective abbreviations, are frequently used in scientific literature. Strictly speaking, GLPC is the most correct terminology, and is thus preferred by many authors.

Usage examples of "gas chromatography".

He turned to the toxicology section, which had graphs of the results of the gas chromatography-mass spectroscopy of blood, cerebrospinal fiuid, and urine.

Under both the common EMIT drug screen and the more sophisticated gas chromatography mass spectrometry, my urine tested positive.

Microscopy, infrared spectrophotometry, pyrolysis-gas chromatography, mass spectrometry, x-ray fluorescence, and neutron activation analysis were not required to figure out that much.

She had oohed and ahhed over a generous assortment of electron microscopes, incubators, radiation counters, test tubes, petri dishes, titration setups, gas chromatography equipment, MRI scanners, and other apparatus she couldn’.

The instrument that was the closest was the giant gas chromatography unit, and Victor decided that he’.

There were plenty of genome readers, scanning probe microscopes, and gas chromatography units, but the big jars of distilled water on the lab shelves had all vanished.

The volatile component of the tholin was examined by sequential and nonsequential pyrolytic gas chromatography and mass spectrometry.

Interpreting the results of gas chromatography on unknown compounds is difficult at best.

But the old priest had described the detonation, and they'd found traces of the event in the surface of a butcher block, verified by gas chromatography.