Development techniques overpressured layer chromatography

New standardized development techniques, i.e., overpressure layer chromatography (OPLC), automated multiple development (AMD), optical detection for development stop... 

Steroids have been extensively investigated using instrumental techniques such as overpressured layer chromatography (2,4,17,34,55), parallel development TLC (56), programmed multiple development [57], and automated multiple development/AMD (58). Each technique has been reported to furnish a significant improvement in separation selectivity in comparison with development in conventional TLC chamber systems. 

At present attempts are being made to optimize the chromatography, and a great deal of faith has been placed in OPTLC (overpressured thin-layer chromatography). With this technique an extension of the development distance, better resolution and a shorter separation time are achieved. In 1982 a report was published on the applicability of this technique in the analysis of various substance groups 59). 

These limitations have led to the development of forced flow development systems and to the technique of overpressured thin layer chromatography. The special feature of this method is that the adsorbent layer is in a completely sealed unit and the solvent is delivered under pressure at a controlled oniform flow-rate by a pump module as in HPLC. Thus, overpressured TLC (OPTLC) takes place in the absence of a vapour pressure and the migration of the solvent front is free from both evaporation and adsorption effects. As the eluant is delivered under controlled conditions it is possible to optimise the separation conditions by adjusting the flow-rate of the eluant and also to undertake continuous development proeedures. 

During recent years, the problem of optimization of separation techniques in thin-layer chromatography has been tackled in both theoretical treatments (129-133) and in the development of instrumentation (134-136). In overpressured TLC (137) a pressurized ultramicrocham r is used. The essential feature of this chamber system is that, in contrast to the rigid glass plate used in the earlier ultramicrochamber (138,139), the sorbent layer is completely covered by an elastic membrane under external pressure, so that vapor phase above the layer is eliminated. Solvent is admitted into the chamber under overpressure by means of a pump system. This technique essentially combines the... 

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