Gas Chromatography (GC) is a method or process in analytical chemistry which analyze and separate compounds that can be vaporized without complete decomposition. Some of the most typical use is in testing pureness of a particular substance or exclude different components from a mixture. In certain cases, gas chromatography also helps in identifying a compound whereas preparative chromatography in GC is to generate pure compounds from a mixture.
The mobile or moving phase in gas chromatography is usually a carrier/inert gas like helium or even unreactive gas such as nitrogen. Of both, Helium is still the most preferred carrier gas for more or less 90% instruments, however, hydrogen is for better separations
The stationary phase is a microscopic/atomic liquid or polymer layer over an inactive solid within a glass or metal tubing known as a column. The instrument is called a gas chromatograph, autograph or simply a gas separator.
The vaporous/gaseous compounds that are analyzed interact with column walls, caked with a stationary phase. Each compound this way is eluted at the uncommon time which is referred to as compound’s retention time. Comparison of the retention time is crucial for analytical usefulness or effectiveness of the gas chromatograph.
Both gas and column chromatography share likewise principles, however, has numerous prominent differences. The process of splitting the compounds in a mixture is performed between liquid stationary and gas mobile phase. Column through which gas phase moves are found in an oven where you can control the gas temperature.
On the contrary, column chromatography has indefinite or simply no control over the temperature. Within the gas, the concentration of a compound is purely vaporing pressure’s function. All that said, gas chromatography is also known as vapor-phase chromatography (VPC) as well as gas-liquid partition chromatography (GLPC).
Process Gas Chromatograph Analysis
An instrument used for analysis and separation of the chemicals in a complex mixture or sample is known as a process gas chromatograph. It uses a flow-through narrow tube called the column which allows passage of different chemical elements in a gas stream at different rates depending on physical and chemical properties as well as interaction with respective column filling known as a stationary phase.
Chemicals are electronically detected and identified the moment they retreat from the column’s end. Stationary phase in the column separates the chemical components and allow each one to exit at a different time which is termed as the retention time. Parameters that can alter retention time order can be gas flow rate, temperature and column length.
Analyte; that can be a liquid or gas is injected in a calculated volume within the entrance (head) of the column via microsyringe. As carrier gas swishes the analyte molecules through the column, the motion is subdued by adsorption of the molecule either into the column walls or packing materials/content. Progress rate of the molecules along the column depends on the strength of adsorption which itself rely on the type of the molecule and materials of the stationary phase.
As each molecule type has a varied progression rate, several elements of the analyte mixture are separated whilst they move along the column and reach its end at different times (retention time). A detector tracks the outlet stream from the column which allows determination of the component’s amount and time of emission.
In general, substances/components are identified in order of their emergence from the column and retention time of the analyte.