Page 194 - Multidimensional Chromatography

Multidimensional Planar Chromatography 187

Figure 8.15 Schematic diagrams of cross-sections of MD-TLC plates connected in series to
ensure multidimensional separation on stationary phases of increasing polarity; hatched lines,
glass plate; light shading, stationary phase A; dark shading, stationary phase B.

plate can be transferred to the second plate. This arrangement of the stationary
phases can be regarded as multidimensional planar chromatography only if the sec-
ond stationary phase (B) is much less polar than the first (A); otherwise, the second
criterion of multidimensionality is not fulfilled.
On the basis of the principle of grafted TLC, reversed-phase (RP) and normal-
phase (NP) stationary phases can also be coupled. The sample to be separated must
be applied to the first (2.5 cm 20 cm) reversed-phase plate (Figure 8.16(a)). After
development with the appropriate (S T1 ; S V1 ) mobile phase (Figure 8.16(b)), the first
plate must be dried. The second (20 cm 20 cm) (silica gel) plate (Figure 8.16(c))
must be clamped to the first (reversed-phase) plate in such a way that by use of a
strong solvent system (S Tx ; S Vx ) the separated compounds can be transferred to the
second plate (Figure 8.16(d)). Figure 8.16(e) illustrates the applied, re-concentrated

Figure 8.16 Views from above (a–c, e, and f) of coupled RP–NP chromatographic plates
(without lines, RP stationary phase; light shading, NP stationary phase), and schematic
diagram of a cross-section (d) through the clamped plates using a strong mobile phase (S Tx ;
S Vx ) for the transfer of the sample to be further separated.