Concentrating zones

For these reasons Reaktions-Chromatographie [7] ( Chromatographie fonctio-nelle sur couche mince [1,2]) is steadily gaining in importance. Here the reaction, which also then takes on the role of a clean-up step, is performed at the start or in the concentration zone of the TLC plate. 

Estriol Dip the concentrating zone of a precoated H PTLC silica gel 60 plate in a saturated ethanolic solution of Fast Dark Blue R salt, allow the solvent to evaporate, apply the sample solution and dip once [10, 59]... 

Fig. 42 Chromatogram of polycyclic aromatic hydrocarbons on caffeine-impregnated precoated silica gel 60 HPTLC plates with concentrating zone (Merck). The following can be recognized in increasing Rf value. — 1. benzo(ghi)perylene, 2. indeno(l,2,3-cd)pyrene, 3 benzo(a)pyrene, 4. benzo(b)fluoranthene, 5. benzo(k)fluoranthene, 6. fluoranthene.

Samples and reference substances should be dissolved in the same solvents to ensure that comparable substance distribution occurs in all the starting zones. In order to keep the size of the starting zones down to a minimum (diameter TLC 2 to 4 mm, HPTLC 0.5 to 1 mm) the application volumes are normally limited to a maximum of 5 xl for TLC and 500 nl for HPTLC when the samples are applied as spots. Particularly in the case of adsorption-chromatographic systems layers with concentrating zones offer another possibility of producing small starting zones. Here the applied zones are compressed to narrow bands at the solvent front before the mobile phase reaches the active chromatographic layer. 

HPTLC plates Silica gel 60 F254S with concentrating zone (Merck), which had been prewashed by developing once with chloroform — methanol (50 + 50) and then dried at 110°Cfor30 min. 

The samples were applied to the concentrating zone as bands in the direction of chromatography. The zones were concentrated by brief development in the mobile phase described below almost to the junction between the concentrating zone and the chromatographic layer, followed by drying for 5 min in a stream of warm air. The actual chromatographic separation was then carried out. 

Layer HPTLC plates Silica gel 60 with concentrating zone... 

It is often possible to carry out any clean-up step that may be necessary in the concentrating zone of a suitable chromatographic plate, in any event clean-up is less complex than for other forms of chromatography. 

TLC plates Silica gel 60 with concentrating zone (Mekck). 1-Propanol - glacial acetic add (90 -i-10). 

Colchicum alkaloids la 344,345,420 Collidine la 354 Concentration zone, TLC plates with la 56... 

In addition, the filament reactor can contain a membrane-separation function by grouping threads of filaments around an inner empty reactor core, that guides the permeate and may also increase permeation by reaction. Thus, the tube reactor constructed in such a way comprises two concentric zones, separated by a permeable Pd/Ag alloy membrane in the form of a tube. The reaction takes place in the filament zone. One product such as hydrogen is removed via the membrane and... 

FIGURE 3.4 Stages of the development of PLC plates silica gel 60 with concentrating zones separation of lipophilic dyestuffs with toluene as the mobile phase, (a) Sample application by dipping in the sample solution, (b) dot-like sample application. 

The most-nsed stationary phase in PLC is sihca gel, with type 60 taking preference. In the fnture, other sorbents snch as the RP materials will also most probably be increasingly nsed. This will also be trae for the case of special PLC plates consisting of layer combinations snch as precoated plates with concentrating zones, resnlting in simphfication of sample application as well as an increase in the efficiency of separation. 

A very helpful tool for manual application can be the employment of layers with a concentrating zone. The so-called concentrating or preadsorbent zone is a small part of the plate that is covered with an inert but highly porous adsorbent such as diatomaceous earth. Various precoated preparative layers with a preadsorbent zone are commercially available. The effect of the concentrating zone is depicted elsewhere in detail (see Chapter 3, Figure 3.4). In brief, the preadsorbent zone serves as a platform for manual application of any desired performance quality. When development starts, soluble components migrate with the mobile phase front and are... 

FIGURE 12.2 Diagrammatic representation of the effect of the concentration zone in preparative separations, (a) Precoated layer without concentrating zone, (b) Precoated layer with concentrating zone. (From Nyiredy, S., Preparative layer chromatography, in Handbook of Thin Layer Chromatography, 3rd ed., Vol. 89, Sherma, J. and Fried, B., Eds., Marcel Dekker, New York, 2003, pp. 99-133. With permission.)... 

Complexation cdiromatography 9ii europium 896 ligand exchange 683, 913 metal terpeneketonates 912 silver ions 911 Concentrating zones (TLC) 676, 726... 

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