08/08/2021

What is Chromatography? How does it work?

Chromatography is the major process of splitting up components of a mixture. The output of the separation is called a Chromatogram.

The chromatography process involves two steps namely the mobile phase and the stationary phase. In the mobile phase, the mixture is dissolved in a substance. This is then followed by the second phase, the stationary phase where the dissolved substance is carried through yet another substance.

In the stationary phase, the different components of the mixture travel at different levels and various speeds which causes the components to split-up. By computing the nature of the mobile phase and the stationary phase, we will be able to conclude on the fastest and the slowest component.

The time travelled by a component is known as the retention time. And, these separated components are collectively known as the Chromatogram. This explanation would have enlightened you with the answer to what Chromatogram is.

Chromatography

In the 19th century, a technique was used to separate pigments from a complex substance or a mixture. For instance, let’s say a container is filled with water or alcohol dissolved with a complex mixture. Now, you take a paper or a cloth and immerse it in the liquid.

Here, a complex, capillary action will take place where the mixture will come in contact with the paper but the components will not travel at the same speed. That is, the largest molecules of the mixture are more rapid than the small ones.

This will cause the stationary phase to exhibit a discrete band of colors depending upon the component properties. This technique is known as chromatography or famously known as “Writing colors”

Chromatography’s travel from art to science

Chromatography was originated from art. It was initially used by color theorists to bring in the perfect shade for textiles, and artists to paint spectacularly amazing paintings. As time went by and the complexity of the technique spawned, Chromatography became a branch of chemistry itself. In today’s world, it is used to analyze complex mixtures and purify them.

Modern laboratories have given up on the color aspect of chromatography. However, the same old principles are in place. Just by dissolving a complex mixture in a mobile phase, it will be transported to the stationary phase where the mixture can be bifurcated depending on their travel speed that is, their retention time.

You will be able to create a wide range of Chromatography methods just by altering either the mobile phase or the stationary phase. Some methods have been devised even by altering the different level of speed of the components.

These methods serve different purposes and are ideal for various mixtures. Listed below are some of the common forms of chromatography.

Gas chromatography

In gas chromatography, the ideal mixture is vaporized and carried through the stationary phase. Note that in gas chromatography, the stationary stage component will usually be either a metal or glass separation column. The mixture is carried via the stationary phase with inert gases like helium or nitrogen. While performing this, you may note that the larger molecules take a much longer time to pass through the separation column and reach the detector.

Liquid chromatography

In liquid chromatography, the mixture is dissolved in a liquid and transported through the stationary phase which might be predominantly solid made of silica. Depending on the polarities of the two different phases – mobile and stationary, there are various varieties of chromatography methods.

Another attribute that influences the method of chromatography is the pressure in the mobile-phase.

Thin-layer chromatography

The mixture is dissolved in a liquid in the mobile phase and transported through a stationary phase which is a thin layer of silica-based solid material. The advantage of this type of chromatography is that the output is easy to digitize.

Ion exchange chromatography

This type of chromatography is used to separate the components of the mixture based on their ions. That is, the positively charged and negatively charged ions are separated using different stationary phases.

Chromatography is basically an analytics tool. You have to just feed the output from the chromatography into the detector to get the contents of the mixture. You can use chromatography as a purification tool also.

The difference between these two usages of chromatography is that the one that is used to read the output requires more quantity of material than the one that is used for purification.

Chromatography can be refined further for using it for a wide array of things. It is believed that chromatography will spawn new variations and pave way for new implementations.

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