PURIFICATION OF SILICA GEL-G LAYERS
The iron present as an impurity in silica gel-G affords an appreciable distortion of the ‘chromatogram’. Hence, it has become almost a necessary step to purify the adsorbent. The ‘iron-free’ layers may be achieved by providing the pre-coated and air-dried plates a preliminary development with a mixture of methanol and concentrated hydrochloric acid* (9 : 1). By this process the entire iron gets migrated with the solvent front to the upper boundary of the TLC plate. Consequently, the purified plates are again dried and activated at 110°C.
The cleaning process usually washes out the CaSO4 originally present as binder. Therefore, the silica gel thus obtained by purification may be reused to prepare TLC-plates with other appropriate binders like gypsum, starch etc.