Adsorption Chromatography: Applications & Types

Instructor: Laura Foist

Laura has a Masters of Science in Food Science and Human Nutrition and has taught college Science.

In this lesson, we will learn about the three types of adsorption chromatography and we will also learn the pros and cons of each type and how they are applied.

Purpose of Adsorption Chromatography

On the back of most medication packages, you will see a list of instructions. Some of these instructions include how frequently you should take the medication and the maximum dosage. How are these times and dosages determined? Part of the process is by determining the concentration of the drug in your system after a certain amount of time. The concentration of the drugs in your system can be determined via adsorption chromatography.

Adsorption chromatography has many applications. Generally, it is used for determining the concentration of a compound (or its purity), separating out a mixture into individual components, and identifying what is in a mixture. There are three main types of adsorption chromatography - column, thin layer, and gas-solid.

Column Adsorption Chromatography

Column adsorption chromatography uses a column packed with the solid stationary phase, a liquid (the mobile phase) runs through this column and specific molecules will adsorb to the solid. Some components will adsorb more readily (or stronger) than other components. The compounds that absorb stronger will form a line first, at the top of the column. Compounds that absorb weaker will form a line towards the bottom of the column. Compounds that aren't adsorbed at all will simply run through the entire column and collect in a beaker at the bottom.

Additional solvents are then added to the column, one at a time. The first solvent can break the weakest interaction between the mobile and stationary phase, bringing that compound with it into the collection beaker. Stronger and strong solvents are added until all of the compounds have been eluted (run through) the column.

Column chromatography will separately collect each compound based on how strongly it adsorbs to the stationary phase
Column chromatography

Drug testing can be performed using column adsorption chromatography. Urine, or other body samples, are run through the column, where the high pH of the urine makes it elute out first, followed by other substances. The other substances that elute out can be tested to see if any drugs are present. The nice thing about this type of chromatography is that the separated out substances can be used for further testing.

Thin Layer Chromatography

Thin layer chromatography (TLC) uses a piece of glass (or other substance) layered with a thin layer of a solid such as silica or alumina. The method behind how TLC works is very similar to how the column works. Compounds that have a strong interaction to the solid won't travel very far along the plate while compound with a weak interaction will travel further along the plate.

In order to use the TLC plates, we first need to have a known sample and test how far the components in that sample will travel on the TLC plate. This is called the reference or standard. We can then compare our unknown samples to the reference plate. If the spots in the unknown sample traveled at the same distances as the known sample then they are the same compounds in the samples.

On the TLC plates the compounds will separate out, with each compound traveling different distances on the plate
TLC

TLC is particularly useful for comparing samples because we can easily see if two samples are the same. The biggest benefit of TLC is that it does not require much space or equipment. In order to test the purity of your drinking water scientists may take a sample of it and put it onto the TLC plate. If the Rf values (how far it travels) are the same as for clean water, then the water is clean, but if there is an Rf value that is different, the water is contaminated.

Gas-Solid Chromatography

Gas-solid chromatography is different because it uses a gas instead of a liquid as the mobile phase, which can adsorb onto a solid. In order to use this method, the solid phase is coated on the inside of a very thin column. This column is put into an oven. Often a substance called diatomaceous earth is used as the solid (stationary) phase.

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