Impregnation by Predevelopment

It is not always possible to obtain good separations of antibiotics of the tetracycline type on TLC plates impregnated by spraying. Oka describes the alternative method of predevelopment with saturated aqueous Na2EDTA solution followed by activation for 2 h at 130 °C [22a]. Eight tetracycline antibiotics are separated by TLC using various solvent systems. 

In the following example, taken from the literature, a significant improvement in the separation and subsequent quantitative evaluation could only be achieved by 

In connection with this example, it should also be pointed out that publications on TLC only make sense if all experimental conditions are quoted correctly. Nyiredi, in an editorial in the Journal of Planar Chromatography (JPC), which he edits, hsts the information that must be provided if scientific contributions to the JPC are to be given any consideration in the future [26]. 

Normally, impregnated TLC plates are only used for special separations, i.e. rarely, so that commercially produced plates of this type would be too expensive. Thus, A. Koch describes the separation of plant hpids on 5 x 5 cm HPTLC sUica gel 60 plates which were impregnated with 0.5 % phosphoric acid especially for this application [27]. The six relevant polycyclic aromatic hydrocarbons are tested for rather more frequently in the monitoring of drinking water. An HPTLC precoated layer impregnated with caffeine is manufactured commercially especially for this apphcation. 

Used parts of the plant (A) upper parts of the flowering plants, dried As (A) plus roots As (A) plus roots 

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Figure 23. Influence of impregnation (by predevelopment with the solvent system) on the liKf values of greater celandine substances...

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