Friday, December 9, 2016

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.

Monday, January 25, 2016

Flash Chromatography Works Better With Silica Gel

What is Flash Chromatography?

In the traditional chromatography method, the sample, which is placed on top of the vertical column, moves at a very slow rate. This results in a lot of time being consumed in separating the different components of the original mixture. As the sample's downward movements are prolonged, one will have to wait a long time before securing the final segregated components.

It is to solve this problem of time consumption that flash chromatography is now being considered as an alternative. Flash chromatography is the best solution to the time consumption problem one faces while working with the traditional column chromatography method.  

Flash chromatography works by the means of air pressure being applied on the solvent to make it move faster through the vertical column. As the pressure is applied, the solvent speeds up its movement through the stationary phase and mobile phase. The separation of the components also, therefore, happens faster than before. With the help of flash chromatography, the complete procedure is done in less than 15 minutes. That is a lot of time and money saved.

Flash chromatography is important for pharmaceutical and healthcare industries where it is used in research about existing and new drugs, cleaning up samples and separating products.

Silica Gel in Flash Chromatography

Silica Gel is the most preferred adsorbent while conducting the Flash Chromatography method. For flash chromatography to yield successful results, it is important the correct adsorbent is used. This is why companies always choose Silica Gel. Other adsorbents that are also used include Florosil, Alumina and reverse phase Silica.

The main reason why Silica Gel is most preferred for Flash chromatography is because it has a high absorption area and even-sized pores. The same-sized pores do not allow the impurities to pass through and only the mixture moves forward. The adsorbent particle size of Silica Gel also plays an important role as this decides the movement of the solvent through the glass column.

The particle size is another point of difference between column chromatography and flash chromatography. While column chromatography makes use of Silica Gel with large particle size, those with small particle size are preferred in flash chromatography.