Thin-layer chromatogram development with a moving pipette delivering the mobile phase onto the surface of the adsorbent layer

The new approach to the development of thin-layer chromatograms is presented. For the first time we show flexible mobile phase dosage onto the surface of the adsorbent layer by moving pipette combined with precise syringe pumps. The pipette is driven into movement by computer controlled 3D machine (modified 3D printer mechanism). Delivery of the mobile phase to the adsorbent layer is equal to or lower than that of conventional development. Therefore chromatograms can be developed with optimal mobile phase velocity, adjusted to its absorption rate by the adsorbent layer. Under such conditions there is no excess of eluent on the surface of the adsorbent layer so higher performance of the chromatographic system can be obtained. Moreover chromatograms can be developed with constant linear mobile phase velocity and therefore the relationships the plate height vs. mobile phase linear velocity obtained with planar chromatography driven by capillary forces are investigated and reported. In addition the contribution of starting spot variance in total peak variance and the influence of narrowing of starting spots on performance of the chromatographic system have been studied. The results confirm a very significant starting spot variance contribution to total peak variance and consequently considerable influence of starting spot size on plate height of the separation system, when chromatogram is developed on a short distance. In the paper the advantages and disadvantages of the prototype device and its possible application are discussed. (C) 2018 Elsevier By. All rights reserved.