Chromatography is a technique employed in laboratories to separate the mixture of chemical components. There are different chromatography types, namely gas chromatography, thin-layer chromatography, column chromatography, paper chromatography, and so many other types. The one common principle used in all these techniques is the Mobile phase and the stationary phase.
Mobile phase: The mixture containing different chemical components is dissolved in a fluid, gas, water, or solvent. This dissolved solvent is known as the mobile phase.
Stationary phase: The fixed, non-moveable medium through which the mobile phase passes is known as the stationary phase. The stationary phase can be a paper, capillary tube, or plate, and it varies according to different chromatography techniques.
GAS CHROMATOGRAPHY :
Gas chromatography is a technique employed to separate, identify, and quantify the organic mixture’s different components. Gas chromatography is further classified into two types, namely Gas-Liquid chromatography (GLC) and Gas-Solid Chromatography (GSC).
Like all other chromatography techniques, this technique’s mobile phase is known as the carrier gas. The stationary phase used in this method is a column whose walls are covered with liquid absorbent. The carrier gas is injected in the column with the required proportions of fuel gas and zero air, which helps combustion of flame and vaporize the compounds passed through the detector.
The gas chromatography is suitable for components having specific attributes for separation like as follows.
- Low molecular weights
- High volatility
- Thermal stability
THE PROCESS OF GAS CHROMATOGRAPHY
The carrier gas is injected into the sample injector’s heated block, which vaporizes the compounds as soon as injected and flows through the column. When the carrier gas passes through the stationary phase, the components get absorbed based on their absorption rates, ion exchanges, partition, or sizes and get separated.
The column through which the carrier gas passes is covered by a column oven that regulars the desired temperature for the separation process. As it passes through the column, the detector is used to measure the chemical components’ quantity and retention factor accordingly.
During earlier days, the equipment used to separate chemical components using the gas chromatography technique had many operating switches and connections for the process’s proper functioning.
Now, with advanced technology, the whole process is controlled by the data system. A data system controls functional parameters like injection series, wash cycle, over-temperature control, the flow of gases, and detector wavelength. The data system also displays every function accordingly and alerts the individual.
TYPES OF GAS CHROMATOGRAPHY
GAS – LIQUID CHROMATOGRAPHY:
In the Gas-Liquid chromatography, the stationary phase used will be an active liquid absorbent. This liquid absorbent is coated with inert support in the column. The stationary phase used here is nonvolatile.
The commonly used liquid stationary phase is dimethyl silicone, polyethylene glycol, 50%phenyl methyl silicone, diethylene glycol succinate in GLC. The solid support used here is fire bricks, glass powder, black carbon powder, and so on.
This inert coating helps to react with the carrier gas and absorb the components according to each chemical component’s varying factors. The temperature maintained in the column ranges from 45 °C – 250 °C. A wide range of chemical elements can be separated in GLC by applying a broader coating column.
It can separate and quantify components with higher concentrations. It also can calculate the retention peaks with good resolution. The tube in which the stationary phase filled is about 30m – 100m in length. The diameter of the tube is about 0.1mm – 0.53mm.
GAS – SOLID CHROMATOGRAPHY:
In Gas-Solid chromatography, the stationary phase used is a solid absorbent. The commonly used stationary phases in GSC are silica, activated carbon, alumina, and molecular sieves. Some organic polymers are also used in this technique, namely porous polystyrene.
The stationary phase filled in the column will be in an active powdered state. These active solid adsorbents are filled in the tube up to 10m in length, and the diameter is about 2-4 mm. The GSC can only process lesser components at a time comparatively to GLC.
ADVANTAGES OF USING GAS CHROMATOGRAPHY:
- This Gas chromatography has been employed in various industries like pharmaceuticals, food, life sciences, forensics, cosmetics, and research institutes.
- Gas chromatography can separate complex mixtures like petroleum or smoke, which has many components in it.
- In gas chromatography, you can control operational functions like gas flow, temperature, and retention peaks.
- It can resolve and analyze volatile compounds efficiently.
- It has high gradient detectors like flame ionization, thermal conductivity, electron capture detectors, and many more.
- There is the freedom to select the stationary phase according to the range of the mixture.
- In gas chromatography, the column can be reused multiple times. The column doesn’t have to be discarded like other chromatography techniques.