Silica Gel: One of the Inorganic Substrate of Flash Columns

The basic material of the stationary phase of the flash columns called substrate is usually divided into three categories: inorganic materials, organic materials, and composite materials.

Silica gel (standard silica gel flash columns, superior silica gel flash columns) is the widest material used to make a matrix in flash columns. Silica gel used in the flash columns usually has a porous structure, which has high mechanical strength and thermal stability. Its surface contains a large number of active hydroxyl groups because of the excellent pore structure and specific surface area. It plays an important role in the purification and separation of compounds in the normal phase purification system.

At the same time, the surface of silica gel can be easily modified to form other bonded stationary phases. And there are many kinds of stationary phases modified by silica gel substrate, and the effect of the separation and purification is much better than other kinds of substrates.

However, the stability of silica gel substrates is relatively poor under alkaline conditions. Not only that, but the presence of hydroxyl groups will also cause irreversible adsorption of some substances, especially alkaline substances.

The non-specific adsorption or denaturalization of the sample appears in the separation and purification of some biological molecular samples, resulting in the difference of peak deformation of sample elution in the chromatogram and the decrease of sample recovery.

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The Use of Silica Gel Flash Columns

Laboratory data show that the optimum flow rate of silica gel flash columns is decided by the length and width of columns and the property of gel. To be more specific, longer, and narrower columns will provide more theoretical plates that are able to affect the flow rate. When referring to the resolution, it is influenced by the stationary phase.

If the stationary phase or the gel which is arranged in the columns is more balanced and with smaller particle size, the silica gel flash columns can provide better resolution. In general, the smaller particle size and the larger superficial area mean higher resolution.

Managing all the factors to optimize the purity of components and the recovery of silica gel flash columns could be very complex because they have a mutual effect. However, different results will be made when in independent testing. In other words, the selectivity of the mobile phase has the most profound effect on separation, but it is also decided by the volume of columns and the selection of solvent.

In fact, before the start of any true experiment, settings of silica gel flash columns need to be tested or calculated. If the data from TLC are available, then the optimal settings can be calculated.