TABLE OF CONTENTS In this procedure the silica gel slurry that is normally used to prepare the layer coating for application on to the glass backing is initially pretreated with the impregnation reagent. Solutions of buffers, complexing reagents, acids, bases, salts, or water-soluble organic compounds are effective for this type of impregnation technique. Once the modified slurry has been prepared it can then be coated on to the backing plate in the usual way. The technique is limited to water-soluble agents. Because preparation of TLC plates in the laboratory is now rarely done, this is not a popular technique.
This can be performed in three ways:
Immersion of the pre-coated plate in a solution (usually 5 10%) of the impregnating agent dissolved in a suitable volatile solvent. The solvent is then evaporated off either at ambient or elevated temperature.
Spraying a solution of the impregnation reagent on to the plate and then removing the solvent as before.
Blank development of the TLC plate in a chromatography tank using the solution of the impregnation reagent as the developing solvent. Migration would be allowed to proceed until the solvent front had reached the top of the layer, and for some time after this so that the "real" solvent front had migrated sufficiently. The solvent is then removed as before.
At times acidic silica gel layers have been used to separate reactive acidic compounds (phenols,...
