Thin Layer Chromatography - Thin Layer Chromatography Chambers 4

 

There are two main effects that results from the pre-saturation of a TLC plate. These affects are depicted in the two plates shown in figure 5. Firstly the velocity of the solvent front is increased relative to that of the unsaturated plate. Secondly, as a significant amount of the stronger solvent components at the solvent front is adsorbed onto the silica surface of the unsaturated plate, the solutes elute much closer to the solvent front. Consequently, the apparent advantage of a faster moving solvent front on the pre-saturated plate (that will reduce the analysis time) is offset by the closer proximity of the spots to the solvent front in the unsaturated plate and a consequent reduced resolution. As a general rule, the effect of pre-saturation on the actual resolution is small but can be important for special mixtures where subtle changes in retention can make an important difference. An alternative apparatus for preconditioning a TLC plate with a solvent other than that used for development is shown in figure 6.

Figure 6. Alternative Apparatus for the Pre-Equilibrium of a TLC Plate