Breakthrough in TLC chromatogram development

Dr Matthias Loppacher looks at a thin-layer chromatography solution to control environmental factors to a level where reproducible and standardised results can be achieved.

Thin-layer chromatography (TLC) is a very flexible but open system and therefore easily influenced by environmental effects. Chromatogram development is the most critical step of the TLC process, particularly because the activity of the layer, chamber saturation, or pre-conditioning of the plate is influencing a specific separation. Up to now one had to pay for the flexibility of TLC by accepting limited reproducibility of results due to those influences.

CAMAG's new Automatic Developing Chamber (ADC2) with a closed loop conditioning and drying process has been developed taking advantage of the principle of Bernoulli. The air in the closed loop system is conditioned, which means the relative humidity is set to a constant, well defined level.

After conditioning, the transfer of moisture to the TLC layer (or back) is achieved by accelerating the air stream to a high velocity across the surface of the layer, thus achieving short transfer times of a few minutes.

Depending on its current activity state the TLC plate will adsorb or desorb water until equilibrium with the air stream is reached.

Finally the air stream is recycled and feed back into the conditioning unit. The closed loop offers the advantage that the air stream can easily be kept clean and a compact, effective system can be built.

If connected to an outlet the described process is showing excellent performance in rapid and heatless drying of the plate after chromatography, which will instantly stop any diffusion. This is of particular interest as any diffusion, which occurs as long as the chromatographic layer is still wet, will unnecessarily broaden the substance peaks in the chromatogram.

Last but not least full compatibility of all methods developed for conventional Twin Trough Chambers can be used without any change. Manual operations, which may be critical and difficult to repeat in daily routine have now been automated. The opening of the chamber during manual development as well as all other human and environmental influence factors have been eliminated.

This new system allows the most effective conditioning of the TLC plate prior to the development, setting up standardised and reproducible parameters. The relative humidity, which is rarely controlled in laboratories, now can be maintained within narrow limits. As a result, chromatography performed in humid summers or coastal climates can be compared to such performed in dry winters or in the highlands. Favourable chromatogram comparisons can be ensured at all times and all places while keeping the flexibility TLC is known for.

Dr Matthias Loppacher is Head of Research & Development, CAMAG, Muttenz, Switzerland.

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