Tuesday, March 10, 2015

Silica Gel Mesh for Column Chromatography

Column chromatography is now regarded as one of the very significant and widely utilized techniques for the analysis and separation of complex organic mixtures. Silica gel for carrying out column chromatography is available in different particle size desired for pilot plant application. The silica gel 200-400 mesh size is ideal for flash chromatography, which means low pressure chromatography. The very smaller size particle of 200-400 mesh size offers better separation outcome with pressurized column. This is the very commonly utilized mesh size in places like organic synthesis labs. The silica gel of mesh size 200-300 is suited for achieving gravitational chromatography. The larger particle size of this silica gel enables solvent to smoothly flow without pressure besides offering excellent separation results.

In column chromatography of 100-200 silica gel grade, a solid adsorbent and the stationary phase is placed in the vertical glass column and a liquid, the mobile phase, is included at the top and flows through the column. The technique of column chromatography is normally employed as a purification process as it isolates necessary compounds from the mixture. The mixture to be examined by column chromatography is placed at the top of the column. The eluent (liquid solvent) is then passed through the column by means of gravity or by application of air pressure. Equilibrium is established between the solute that is adsorbed using adsorbent and the solvent flow down via the column. As the various components in the mixture possess various interactions with the mobile and stationary phases, they are carried along with mobile phase to different degrees and thus a separation is attained. The elutants or individual components are collected from the bottom of column as solvent drips.

The silica grade considerations for column chromatography should be made according to the specific requirements of the application. The silica gel of high purity grade provides lowest moisture content, minimal impurities, tightest particle size distribution and greatest consistency. This leads to greater reproducibility of separation process. The technical grade silica gel is regarded as the most economical option for general separations, where lot to lot consistency and reproducibility are not as crucial.