Preparative OPLC Separations

Whether or not the use of OPLC for preparative separation is necessary depends on the kind of sample to be separated. The potential of linear online OPLC on 20 cm x 20 cm plates with a separation distance of 18 cm as a preparative method is considerable. Because the average particle size of pre-coated preparative plates is too large, not all the advantages of this method can yet be realized. Generally, preparative online OPLC can be used for separation of 6-8 compounds in amounts up to 300 mg.

Figure 6 Micropreparative ML-OPLC separations on analytical HPTLC plates. (A) Schematic diagram of cleanup procedure using fully online LD-OPLC; (B) schematic diagram of fully online LD-OPLC for a large amount of a complex mixture.

polymer suspension, resulting in faster migration of part of the mobile phase, because of lack of layer resistance; the mobile phase then re-enters further along the plate ('break-in effect' as shown in Figure 7A). This reduces the value of the separation, at least at the edge(s) of the layer.

If the area impregnated is too wide, i.e. the edges of the stationary phase covered by the polymer suspension are wider than approximately 1 mm, the 'meniscus effect' can occur (see Figure 7B). As a

Figure 6 Micropreparative ML-OPLC separations on analytical HPTLC plates. (A) Schematic diagram of cleanup procedure using fully online LD-OPLC; (B) schematic diagram of fully online LD-OPLC for a large amount of a complex mixture.

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