Silica gel is the most commonly used desiccant in the food and pharmaceutical packing industry. It is US FDA approved and also very safe. Silica gel is also called silica aerogel or hydrated silica. Silica gel, along with being a good desiccant in food packaging industry is also used in many procedures in chemistry. It is used in chromatography as a stationary phase. Different particles of different sizes are used for achieving a desired separation of certain molecular sizes in the process of column chromatography. Silica Gel Powder is used in Pharma & Chemical Research Laboratories for column chromatography.
In column chromatography, the stationary phase is most often composed of silica gel particles of 40–63 μm. In column chromatography, due to silica gel’s polarity, non-polar components tend to elute ahead ofother components which are much more polar. Hence it is named as normal phase chromatography. However, when hydrophobic groups (such as C18 groups) are attached to the silica gel then polar components elute first and the method is referred to as reverse phase chromatography. Sometimes Silica gel is added to aluminum, glass, or plastic sheets for thin layer chromatography.
The Column of the chromatography column is packed in the following manner for the procedure- it is plugged with a small piece of cotton wool, just enough to fill to stopcock hole.2 cm sandis added so that the diameter of the sand is approximately the same as the column. Then Silica gel is added dry. Usually, length of the silica is not too long, approximately 6 to 10 inches is best.Sandis added to the top of the column, about 1-2 cm. Then the solvent is poured and allowed to flow through the column until it is eluting. If the solvent is forced down the column by positive air pressure, it is called flash chromatography because it can be done in a flash.
These silica gel adsorbents are sold in different mesh sizes of 200-400 mesh and 230-400 mesh . This number refers to the mesh of the sieve used to size the silica, particularly the number of holes in the mesh or sieve through which the crude silica particle mixture is passed in the manufacturing process. Silica gel is used as an absorbent in the Purification (Isolation) and Separation of organic chemicals compounds and Chemic Synthesis process.