Topics - Loading
In chromatography the term loading can have two meanings. It can either refer to the amount of sample that is placed on the column, or it can refer to the amount of stationary phase placed on the column (in a packed column it may refer to the amount of stationary phase carried by the support). When the term loading refers to sample size it is usually in the context of preparative chromatography. Obviously the loading of a preparative column may be critical as it must be as large as possible without denigrating the quality of the separation. In a similar way the loading of stationary phase
on a column may also be critical, as it determines the film thickness which, in turn, determines the magnitude of the resistance to mass transfer in the stationary phase and, thus, the column efficiency. In fact, for a given solute pair, retained at specific capacity ratios, there will be an optimum film thickness
that will allow the separation to take place in the minimum time (i.e., there will be a critical stationary phase loading
). In general the stationary phase loading on a capillary column will range from a film thickness of about 0.1 to 0.5 micron. The loading of stationary phase on the support of a packed column will range from about 4% to about 15 %.