What is Gas Chromatography Testing?
Gas chromatography testing, also known as GC is one chromatography testing method. Gas chromatography is defined as an analytical separation technique where the minor components in a mixture of gases are separated and resolved into individual components.
In this testing method, the mobile phase is a carrier gas (usually an inert gas like helium or an unreactive gas like nitrogen) and the
stationary phase is a microscopic layer of liquid on an inert solid support inside a glass or metal tubing
(called a column).
Gas chromatography testing has many applications. For instance, the GC test may be used to determine the quality of products for a chemical company or to measure toxic substances present in air, soil or water. It is an extremely accurate test and can determine parts per million in most substances.
Components Required For
Gas Chromatography Testing:
Detector – Various detectors are used in gas chromatography testing. The detectors are typically sensitive to a range of components and will work over a range of concentrations.
Carrier Gas – The carrier gas used during the mobile phase is very important. Hydrogen is most widely used as it is efficient and provides excellent separation. Helium is also used because it has a large range of flow rates and is non-flammable.
Column – There are two different types of columns used in gas chromatography. A packed column is 1.5-10m long and has an internal diameter of 2-4mm. The tubing is made of stainless steel or gas. Capillary columns have a smaller internal diameter and the inner column walls are coated with active materials. Capillary columns are flexible so a very long column can be wound into a small coil.
Column Oven – The columns for gas chromatography are located in an electronically controlled oven. How fast a sample passes through the column is directly proportional to the temperature of the column. For example, the higher the column oven temperature, the faster the sample will move through the column.
Autosamplers – The autosamplers provide the way to automatically introduce a sample into the inlets.
Inlet/Injector – provides the way of introducing a sample into a constant flow of carrier gas. The inlet is the hardware piece that is attached to the column head.
All of these components are necessary for the transmission of the gas sample through the column using the carrier gas. As noted, the column is coated with a material for which the gases to be separated have an affinity and the strength of the affinity determines the time any component is retained in the column. Detectors are employed in this testing method like specific compound responsive detectors or generally sensitive detectors.
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