Preparative Chromatography - Radial Flow Chromatography > Page 62

The core houses the inner frit, through which the eluent percolates and exits at the base of the column to a detector and hence to a fraction collector. The outer frit constitutes the column inlet, and consequently the sample has initially an extremely large area of stationary phase with which to interact. This renders the loading capacity of the radial flow column also very high. It is interesting to note, that as the solute progress radially through the stationary phase bed towards the center, the effective cross-sectional area of the column will become smaller. Consequently, the plate volume of the column will decrease (see Plate Theory and Extensions ) as the solute moves to the center which will result in the solute being concentrated. However, as the solute bands progressively decrease in concentration due to normal dispersion processes (see Dispersion in Chromatography Columns ), this counteracts the concentration effect from reduced bed cross-section and prevents the column packing from becoming overloaded at the center.

The sample is injected on the top of the column, where it is dispersed by radial channels (see figure 32.) to ensure an even sample loading around the periphery of the column. Although this type of column has a high capacity, it is also relatively short and thus not suitable for complex mixtures that need to be developed isocratically. They can, however, be used very effectively with gradient elution.