Page 196 - Multidimensional Chromatography

Multidimensional Planar Chromatography 189

(LD)-OPLC, involves the serial connection of the chromatographic plates. By appli-
cation of this technique, it is also possible to use different stationary phases of
decreasing polarity during a single development, as shown in Figure 8.18(a).
Specially prepared plates are necessary for this LD-OPLC technique in linear
development mode (35) – all four edges of the chromatographic plates must be
impregnated with a special polymer suspension. Movement of the mobile phase with
a linear front can be ensured by placing a narrow plastic sheet on the layer. Three
plates can be placed on top of each other to create the long development distance.
The end of the first (top) chromatographic plate has a slit-like perforation to enable
transfer of the mobile phase to the second layer, where migration continues until the
opposite end of that layer. Development can then either continue to the next chro-
matographic plate or, if chromatography is complete, the mobile phase can be
drained away. On this basis, 60 cm separation distances can be achieved with
P-OPLC 50 equipment. As a consequence of the manner in which the layers are pre-
pared, glass-backed plates can be used at the bottom of the stack only.
For this technique, the upper plate has a mobile phase inlet channel on one edge
and a slit at the opposite edge for directing the mobile phase toward the next plate
(33). The slit (width approx. 0.1 mm) can be produced by cutting the layers with a
sharp blade; this enables easy passage of mobile phase and separated compounds
without any mixing. The cushion of the OPLC instrument is applied to the upper-
most layer only, and each plate presses on to the sorbent layer below.
The potential of serial connection of layers can be used for multidimensional
planar chromatographic separations on different stationary phases of decreasing

Figure 8.18 Schematic diagrams showing: (a) serially connected multilayer OPLC employ-
ing different types of stationary phase of decreasing polarity (A B C) as a type of MD-
FFPC; (b) fully off-line operational mode; (c) fully on-line operational mode.