Page 180 - Multidimensional Chromatography

Multidimensional Planar Chromatography 173

Figure 8.2 Schematic illustration of a bi-directional, multidimensional planar chromato-
graphic system in which the number of ‘secondary columns’ is unlimited.

expressive; instead, the term ‘multidimensional planar chromatography’ (MD-PC)
should be used.
MD-PC is highly important in its own right, because this is the only real multi-
dimensional separation method in which all compounds can be passed to a next
dimension. It therefore serves as the reference system (7) against which all other
multidimensional systems can be compared.

8.3 TWO-DIMENSIONAL DEVELOPMENT ON SINGLE LAYERS

CHARACTERISTICS OF 2-D SEPARATIONS

The term bi-directional or two-dimensional chromatography has its origin in TLC; it
was defined as chromatographic development in one direction followed by a second
development in a direction perpendicular to the first (8). The method consists of
spotting a sample at the corner of a chromatographic plate (Figure 8.3(a)) and
enabling migration of the mobile phase (characterized by S T1 ; S V1 ) in the first direc-
tion (Figure 8.3(b)). After drying, sequential development of the plate, in a direction
at right angles to the first development (Figure 8.3(c)), can be started with a second
mobile phase, (characterized by S T2 ; S V2 ). The overall separation obtained is superior

Figure 8.3 Schematic illustration of a classical, bi-directional or two-dimensional planar
chromatographic procedure.