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Gas Chromatography

Last updated date: 09th Apr 2024
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What is Gas Chromatography Mass Spectrometry?

Gas liquid chromatography (GC) is an analytical technique for separating chemical components in a sample mixture and then detecting them to ascertain their presence or absence, as well as how much of each component is present. Organic molecules or gases are the most common chemical elements. These components must be volatile, with a molecular weight below 1250 Da, and thermally stable so that they do not degrade in the Gas Liquid Chromatography system, in order for GC to be effective in their study.

Gas Chromatography Mass Spectrometry (GC-MS)

Glc chromatography is a commonly used technique in almost every industry: for quality control in the manufacturing of a wide range of products, from automobiles to chemicals to pharmaceuticals; for testing, from meteorite analysis to natural product analysis; and for protection, from environmental to food to forensics. To allow the identification of chemical components, gas chromatographs are frequently hyphenated to mass spectrometers (GC-MS).

Strengths and Limitations of Gas Chromatography

Gas solid chromatography is a commonly used technique in almost every industry. It's used for anything from routine analysis to testing, analyzing a few to hundreds (or thousands with GC x GC) of compounds in a variety of matrices, from solids to gases. It's a reliable method that can be combined with other methods, such as mass spectrometry.

GC can only analyze volatile compounds ranging from helium/hydrogen to about 1250 u in molecular weight. Thermally labile compounds can degrade in a hot GC, so use cold injection techniques and low temperatures to prevent this. Since more polar analytes can get trapped or lost in the GC, the device should be deactivated and well-maintained, or the analytes should be derivatized.

What are the Different Types of Gas Chromatography?

There are many different ways of using chromatography. These are some of the best known:

Paper Chromatography

This is the classic "spot of ink on paper" experiment from school (also the effect we described at the start when you get your papers wet). Typically, a spot of ink is placed on one of the filter paper's edges, and the paper is then hung vertically with the lower edge (nearest the spot) dipped in a solvent such as alcohol or water. The solvent travels up the paper due to capillary action, where it reaches and dissolves the ink. The dissolved ink (the mobile phase) moves up the stationary phase (the stationary phase) and divides into various components. These are often colored; other times, you must color them by adding other substances (referred to as developers or developing fluids) that aid in identification.

Column Chromatography

Instead of paper, the stationary step is a vertical glass jar (the column) filled with a highly absorbent solid like silica crystals or silica gel, or a solid covered in a liquid. The mobile phase drips (or is pumped at high pressure) through the column, splitting into its constituents, which are then extracted and analyzed.

There are Quite a Few Variations, Including:

  • Liquid-column chromatography is a form of chromatography in which the mixture being examined is put at one end of the column and an eluent (also written eluent) is poured in to help it move through.

  • Thin-film chromatography is a variant of this technique in which the "column" is simply a thin layer of adsorbent material coated on a film of glass, plastic, or metal.

  • The mixture is pushed through the column at high pressure in high-performance liquid chromatography (HPLC) (roughly 400 times atmospheric pressure). This is more concise, quicker, and responsive.

Gas Chromatography

We've spoken about chromatography of liquids passing through solids so far, but one of the most common techniques is a form of column chromatography that uses gases as the mobile step. Gas chromatography is a method of chemical analysis that is largely automated and performed using a sophisticated piece of laboratory equipment called, unsurprisingly, a gas chromatograph machine. 

Gas Liquid Chromatography

Gas-liquid chromatography (also known as gas chromatography) is an analytical technique with many applications. A stationary phase and a mobile phase are used in all types of chromatography. The mobile phase is a liquid in all of the other types of chromatography you'll encounter at this stage.

The mobile phase of gas-liquid chromatography is a gas such as helium, and the stationary phase is a liquid with a high boiling point adsorbed onto a solid. The amount of time a compound spends traveling with the gas as opposed to being bound to the liquid in any way determines how quickly it moves through the pump.

Stationary Phase in Gas Chromatography

First, a small sample of the mixture of substances being analyzed is pumped into the machine using a syringe. The components of the mixture are heated and vaporize almost immediately. Then we add an eluent (carrier), which is simply a neutral gas like hydrogen or helium that helps the gases in our sample pass through the column. In this case, the column is a thin glass or metal tube filled with a high-boiling-point liquid (or sometimes a gel or an adsorbent solid). The mixture is adsorbed and separated into its constituents as it passes through the column. Each part emerges from the column's end and passes through an electronic detector (sometimes a mass spectrometer) that recognizes it and prints a peak on a map. The final graph has a set of peaks that correspond to each of the mixture's constituents. Vapor-phase chromatography (VPC) or gas-liquid partition chromatography are two terms used to describe gas chromatography (GLPC).

Carrier Gas in Gas Chromatography

For gas chromatography, the carrier gas (mobile phase) should be an inert gas that does not interfere with the sample components. The contribution of the GC carrier gas to the partitioning phase should be negligible. In liquid chromatography, this is different from the mobile phase. The carrier gas in GC is simply described as a transporter for vaporized solute molecules through the column during the partitioning process. Compressible gases that grow as the temperature rises are known as carrier gases. The viscosity of the gas changes as a result of this. The carrier gas's linear velocity and selection can influence resolution and retention times. Carrier gases must be inert to the stationary phase and free of pollutants that can be detected.

FAQs on Gas Chromatography

Q1 - What is Chromatography Used for? 

Ans - Mikhail Tswett (sometimes pronounced Tsvet; 1872–1919), an Italian-born botanist, invented chromatography in Russia in 1906 and used it to research plant pigments including chlorophyll. (Because Tswett, like all great scientists, used and improved on techniques created by others, there is some debate on whether he can really be called the "inventor" of chromatography.) Chemists discovered chromatography to be an excellent method for analyzing and separating a wide range of complex mixtures throughout the twentieth century.  It's now commonly used in forensic science (to identify samples collected from crime scenes), environmental testing (to identify small amounts of unknown contaminants in air and water samples), and research into complex mixtures in industries like food, perfume, petrochemicals, and pharmaceuticals. Chromatography has the advantage of working with small samples and low concentrations (particularly helpful when it comes to such things as forensic science and drug or pollution testing).

Q2 - How Does Gas Chromatography Work?

Ans - As the name implies, GC separates using a carrier gas, which serves as the mobile process. The carrier gas moves the sample molecules through the GC device without reacting with the sample or causing damage to the instrument components.

The sample is then injected into the gas chromatograph (GC) using a syringe or transferred from an autosampler, which can collect chemical components from solid or liquid sample matrices. The sample is injected into the GC inlet through a septum which allows the sample mixture to be injected without missing the mobile phase. The analytical column is held in the column oven, which is heated to elute the less volatile components during the analysis. The column's outlet is inserted into the detector, which generates a signal in response to the chemical components eluting from the column. A chromatogram is generated by recording the signal with acquisition software on a monitor.