Analytical RPC Separations

In analytical M-RPC there is a vapour space (1 or 2 mm) between the chromatographic plate and the quartz glass cover plate. In analytical U-RPC a soft crepe rubber sheet is placed underneath the analytical plate so that vapour space between the layer and the quartz cover plate is almost eliminated.

In analytical RPC (M-RPC and U-RPC) three development modes are available and the separation distance and number of samples depend on which mode is used. 20 cm x 20 cm plates can be introduced directly into the instrument. In circular mode (Figure 13A) the most commonly used, up to 72 samples can be applied to an HPTLC plate as spots; the separation distance is usually 8 cm. Despite the centrifugal force, the mobile phase direction of flow can be linearized (linear development mode) by scraping channels in the layer (Figure 13B); this reduces the number of samples. The anticircular mode can also be employed with special preparation of the analytical plate (Figure 13C). Although the solvent is delivered

Figure 13 Development modes in analytical RPC on 20 cm x 20 cm HPTLC plates. (A) Circular; (B) linear; (C) anticircular.

at the centre of the plate, in anticircular mode the amount of stationary phase available during development is reduced according to a quadratic relationship by preparation of the layer.

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