Chromatography Adsorbents - An Introduction
The chromatography process consists of two phases - the stationary phase placed in the vertical column and the mobile phase, which is placed on top of the same column and then makes it way downward. As the mobile phase moves downwards, different constituents of the mixture will get separated at different levels, thus completing the chromatography process.
Adsorbents are very important to the chromatography process. They are basically molecular desiccants with high surface density and large surface area. Adsorbents are used in different types of chromatography for absorbing and thus separating, various components of any given mixture. The commonly used adsorbents include Silica Gel, Alumina, Carbon, Magnesium Oxide and different types of carbonates. Each adsorbent brings to the table its own unique characteristics and benefits.
Why Silica Gel Adsorbents are Important for Chromatography
Silica Gel is one of the most important adsorbents used as the stationary phase in the chromatography process. Among Silica Gel adsorbents, the porous variety is most preferred by the clients. Silica Gel desiccant is known to be an acidic adsorbent and therefore has less polar properties when compared to Activated Alumina. As Silica Gel desiccant is less polar, it will mostly adsorb all the basic compounds present in the mixture.
The particle size of the Silica Gel is what decides, which chromatography process it will be used for. The particle size is directly proportional to the surface area of the Silica Gel. More surface area translates into more water vapour molecules getting adsorbed. This can be explained with the help of few examples- In normal phase chromatography, non-polar components elute quicker because of the polarity of the Silica Gel adsorbents. In reverse phase chromatography, it is the polar components that elute first as hydrophobic groups get attached to the Silica gel.
There are many reasons as to why Silica Gel is preferred as the stationary phase. The first and main reason is its high polarity, which can attract water vapour or any other molecules in the shortest time possible. This makes economic sense for clients as they need not spend too much time and money in choosing the stationary phase adsorbent. The second is its large surface area, wherein more molecules can be adsorbed over more area. The third and final reason is its easy availability in the form of beads, balls and granules.
