Page 199 - Multidimensional Chromatography

192 Multidimensional Chromatography

Figure 8.20 Combination of bilayer plates and multiple development techniques in which
total solvent strength and mobile phase selectivity are changed simultaneously: in the first
direction (a), S T and S V are varied in ‘n’ re-chromatographic steps, while in the perpendicular,
(second) direction (b), S T and S V are again varied in ‘m’ re-chromatographic steps, to give (c).

n
power can also easily be increased by the use of D in the second dimension.
Increasing the dimensions of the separation procedure always increases the number
of theoretical plates, which leads to enhancement of the separation number and,
therefore, the efficiency of the separation.
Satisfactory combination of more than three chromatographic plates for long-
distance OPLC is always difficult, because only the bottom plate can be glass-
backed; the others must be aluminium-backed (32, 33).

Figure 8.21 Schematic diagram of the combination of bidirectional, multiple development
and coupled layers in decreasing polarity (A B C).