Activation of the layer

Acridine orange, pH-dependent change of fluorescence color 91 Activation of the layer 124ff. N-Acylglycine conjugates 176 ADB = 2-amino-2, 5-dichlorobenzophe-none 227... 

One of the most crucial influencing factors in planar chromatography is the vapor space and the interactions involved. The fact that the gas phase is present, in addition to stationary and mobile phases, makes planar chromatography different from other chromatographic techniques. Owing to the characteristic of an open system the stationary, mobile, and vapor phases interact with each other until they all are in equihbrium. This equilibrium is much faster obtained if chamber saturation is employed. This is the reason for differences in separation quality when saturated and unsaturated chambers are used. However, the humidity of the ambient air can also influence the activity of the layer and, thus, separation. Especially during sample application, the equihbrium between layer activity and relative humidity of the... 

SOFC electrodes are commonly produced in two layers an anode or cathode functional layer (AFL or CFL), and a current collector layer that can also serve as a mechanical or structural support layer or gas diffusion layer. The support layer is often an anode composite plate for planar SOFCs and a cathode composite tube for tubular SOFCs. Typically the functional layers are produced with a higher surface area and finer microstructure to maximize the electrochemical activity of the layer nearest the electrolyte where the reaction takes place. A coarser structure is generally used near the electrode surface in contact with the current collector or interconnect to allow more rapid diffusion of reactant gases to, and product gases from, the reaction sites. A typical microstructure of an SOFC cross-section showing both an anode support layer and an AFL is shown in Figure 6.4 [24],... 

The factors affecting Rf include the quality of the stationary and mobile phases, the thickness and activity of the layer, and the amount of sample. Although standards may have the same Rf value as the sample, this does not uniquely identify the compound. For archaeological samples, the best identification achievable is only at a general class level (e.g., triacylglycerols, fatty acids, aromatic, or aliphatic) and not to individual molecular components. 

In adsorption chromatography, high activity leads to high retardation properties of the stationary phase and hence to shorter migration distances of the sample substances than those obtained with less active sorbents. This means that, to achieve reproducible retardation values, a well-defined level of activity of the layer is necessary. 

The electrochemical activity of the layer is checked by changing the solution for the monomer-free electrolyte solution and running cyclic voltammetry. Reversibility can easily be seen from the shape of the curve. 

It must be said in advance that in ion-exchange TLC, the regeneration or activation of the layer and the development of the chromatogram must be distinguished. Regeneration, i. e., conversion into the necessary ion-form, is carried out as far as possible before the material is spread on to the plates it can also be performed on the plate with the solvent or buffer to be used subsequently. In cases of doubt, layers can always be activated with 0.1 N sodium chloride solution. In the examples so far known, chromatograms have been developed with 0.01 to 1.2 N... 

The preparation of layers in general is described on pp. 52—59. Activation of the layer is undesirable, at least for the compound classes treated here. 

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