Variables Defining the Utility of Gel:

After having learnt about the different categories of gels used for chromatographic work, the methods of their preparation and some of the important characteristics, it is necessary to name a few variables which really characterize the utility of gel. The most important of the different properties is the fractionation range. Sometimes, it is given as the upper limit of fractionation or the exclusion limit. When the exclusion limits or the fractionation ranges are provided, it should be begin that for what type of substances these data are obtained. These numbers vary along with one category of substances to another. For a given group of compounds, polysaccharides, say globular proteins, etc. they are fairly constant. The other important variable of significance is the steepness of the selectivity curve in the linear portion of the fractionation range.

For xerogels, the water regain is the common measure of the swelling capacity of the gel. Here, it may be important to tell more about xero gels and aerogels. Different gels react differently to the removal of liquid in them. The group of xerogels shrinks on drying to a compact material containing only the gel matrix. The aerogels, on the other hand do not shrink; instead the surrounding air penetrates into the gel. Xerogels when brought in contact with the liquid take up liquid and return to the gel state. In aerogels also, the air can be substituted by the liquid.