chromatography

In general, chromatography is one of the separation methods commonly used in many applications, where it is used to separate the constituent materials of a sample, from each other.
There are many separation methods in chromatography, and they differ according to the sample whose components are to be separated and the application in which the chromatography is to be used.
Gas chromatography is one of the most popular and efficient types of laboratory equipment used today.

What is gas chromatography?

We previously talked in general about what chromatography is, and how it works, and today it is our turn to talk about one of its types and how to use it. Our talk today will be about gas chromatography, which is used in many important applications, some of which we will mention later.

The name of this type of gas chromatography came because the moving medium that moves the sample materials is gaseous, so there is a gas that moves the sample materials through a tube, and each component of the sample is separated during its movement in the gas.

How it works: As we mentioned before, we generally have two medians in the chromatography: the first is the moving medium that works to transfer the components of the sample with it during its movement, and the second is the fixed medium that does not change in place with time and works mostly to inhibit the movement of the components of the sample. In gas chromatography, as its name indicates, the moving medium is gas, and the sample is also in the form of gas, or it is converted into a gas so that the device can deal with it. The stationary medium is either a liquid or a solid.

At first, the required sample is injected into the device, and it is heated to turn into a gas so that the device can deal with it. After that, the device pumps an inert gas (an inert gas is used so as not to interact with the components of the sample) in order to move the components of the sample from its place through the column (a long tube of small diameter) until it reaches the detector that recognizes the material that reaches it and sends the data to the computer .
In the end, the computer gives us the data in the form of a graph, which we analyze to find out the materials that make up the sample.

This image above shows a simplified form of the device:
on the left is the gas tube that pumps the gas into the tube in order to act as a moving medium. After that, the injector appears, in which the sample is placed, to be injected into the device to reach the spiral tube visible in the picture. This tube is inside a furnace that heats the gases so that they do not condense again. At the end of this furnace, part of the tube comes out to the detector, which infers the materials that reach it.

Components of the machine and how each part works:

Sample entry:

At first, the sample is placed in the place designated for it, then it is heated, and its components begin to volatilize to form a gas. After that, the sample is entered into the duct that contains the carrier gas to be transferred through the device. The sample heating stage can be bypassed if its components are fragile at high temperatures, then they are injected directly into the carrier gas stream.

carrier gas:

The gas that plays the role of the moving medium comes packed into cylinders, and these cylinders are connected to the device to inject the gas into the device. This gas is passed through filters to be purified and to ensure that it is completely pure and that there are no impurities that can interact with the sample materials in one way or another.

The required gas pressure varies depending on the sample being analyzed, and the type of application in which we use the chromatograph. So the gas pressure is always controlled and changed as needed. The type of gas used also varies depending on the type of sample to be analyzed, as hydrogen, nitrogen or helium can be used. It is required that the gas is not able to react with the sample materials so as not to change its properties.

column:

Now we come to the method of separation, in which we separate the material into its main and sub-components. Its idea is quite simple, as we mentioned in a previous article, the basic idea in the separation process is the different ability of each sample material to interact with the stationary phase, where the period of connection between the material and the stationary medium varies according to the properties of the material. Here comes the role of the column that contains the constant medium, where the constant medium here is either a liquid or a solid. The type of shaft used also varies according to the application, as the materials that make up the shaft from the inside differ, and the length and diameter of the shaft vary. A shaft can be used as a long capillary tube or the shaft has a larger diameter and contains some materials inside.

electric oven:

Now we must ask about the role of the oven, which is one of the most important parts of the device.
The furnace controls the temperature of the column so that the sample material does not turn into a liquid again inside the column. The furnace is also used in the event that the boiling point differs between each of the sample materials, as the temperature of the furnace is gradually raised in a manner appropriate to the sample used.

Detector:

Now that the injected sample has reached the end of the road, how will we identify it or how much? Or how will we know that a compound has reached the end of the column?

In fact, there are several methods that are used to detect sample materials. The device that detects the arrival of a substance at the end is called the detector, and there are many types of it, each of which has a different way of working from the other. The detector used varies depending on the application, the type of information we want, and whether we want to do a quantitative or qualitative analysis. Each type depends on some chemical and physical properties of the materials, as it detects the material when its characteristic appears, then amplifies the signal and converts it into an electrical signal that is sent to the computer.

The types of detector are:

Flame Ionization (FID)

Electron Capture (ECD)

Flame Photometric (FPD)

Nitrogen Phosphorous (NPD)

Thermal Conductivity (TCD)

Mass Spectrometer (MS)

Data recording:

When the presence of a compound is detected, the signal is sent from the detector to the computer, which in turn translates the information that reaches it into a graph called the chromatogram, which we can analyze and easily identify the type of compounds.

History of gas chromatography:

The first to use gas as a mobile medium in chromatography were the two scientists, Archer J. Martin and Richard L. M. Synge, in 1941 AD. The two scientists began to realize that the mobile phase- does not always have to be liquid, But it can also be a gas. These two scientists were the first to use gas chromatography as an analysis technique. A gas was passed over a volatile sample, and then passed through a column with (gel) containing a non-volatile liquid. It was found that this separation method is faster in time and more An efficient separation method known at the time.

At first there was not much interest in this method, but the scientist Martin worked more on this method with his assistant and developed the first device that worked in this way.

Gas chromatography uses:

This type of chromatography has many applications, of which we will mention a few here:

First, it is certainly used to serve science, as researchers use it to analyze materials and identify their components, for its great ability to identify materials and the accuracy of the results that the device gives. Gas chromatography can also be used in the pharmaceutical field to analyze drugs and the materials that remain from the drug industry’s residues and to ensure the quality of the produced drug. It is also used in the food field to analyze foods, and is used in the petrochemical industry, in various chemical industries, and in environmental applications to determine the level of pollution in the environment.