|
|
Figure 11. A Two-Dimensional TLC Separation
Similar two-dimensional separations can also be carried out in LC but LC requires each complex peak to be diverted to a second, and different, column (with a different stationary phase and, sometimes, also with a different mobile phase) and a separation carried out for each complex elution band. Thus, although in two-dimensional TLC, the first separation on the first phase system is similar to that in LC, in the second development, all the separate composite peaks or spots are developed simultaneously on the same stationary phase albeit with a second solvent mixture.
In contrast, each composite solute band must be individually separated with two-dimensional LC but a specific optimum solvent mixture or solvent program can be used for each composite peak. It is clear that although the resolution obtained using two-dimensional TLC can be very effective, the ultimate resolving power of two-dimensional LC will be far greater (and, of course, the equipment will be very much more expensive). | |
