Which Adsorbents Are Superior in Chromatography?

Chromatography and Its Different Types

Chromatography is a commonly used method for the separation and purification of different mixtures. It basically involves two steps- the mobile phase and the stationary phase. The chromatography process is explained as follows- at first the mixture, which has to be separated is dissolved in the liquid mobile phase and then placed on top of a vertical glass column. Then it is passed down the vertical column containing the solid stationary phase. As the mixture makes its journey downwards, different components will get separated at different levels. This is because different components move at different speeds and this is the reason behind their separation. The latter is also dependent on the differential partitioning between the mobile and stationary phases.

Chromatography is broadly divided into preparative and analytical. While preparative chromatography is used to isolate the components of any given mixture for further use, analytical chromatography uses smaller amounts of material. This form of chromatography is mainly used for measuring the relative proportions of analyses in a mixture. Based on other parameters, chromatography is also categorized into thin-layer chromatography and column chromatography. Both these methods are helpful in separating different components of mixtures.

Adsorbents Used in Chromatography

The stationary phase of the chromatography process makes use of a thin layer of adsorbent like Silica Gel, Alumina and Cellulose on a flat inert substrate. Companies make use of high-quality adsorbents because it will take in all the different components at different levels. Adsorbents are clearly preferred over simple paper as it can absorb faster and thus ensure better separations.

Which Adsorbent is Superior?

Each adsorbent has its own advantages and disadvantages when being used in the chromatography process. While Silica Gel is readily available in beaded, granular and ball form, there are some benefits of using Alumina adsorbent. Silica Gel as an adsorbent has a larger sample load and thus can absorb more effectively. However, Activated Alumina showcases amphoteric properties and is known to act as a weak ion exchanger.

Silica Gel Adsorbents hydrolyzes at temperatures more than 40 degrees Celsius and that too in the presence of phosphates and carbonate ions. Another advantage of using Silica Gel adsorbent is that it dissolves in aqueous/organic media and slightly alkaline media at high temperatures.

Even though Silica Gel has the above mentioned advantages as an adsorbent, Activated Alumina is considered superior because the latter has excellent pH stability over Silica Gel. Activated Alumina is also best suited for reverse phase chromatography and for the preparation of chemically bonded C18 phases and other ligands.