Silica gel impregnated with silver ions has been successfully used in the separation of unsaturated compounds by thin-layer (TLC) and column chromatography [6-23]. However, no significant modification of the preparation of this kind adsorbent has been introduced.
The reported procedures [8,15,18,20,21,23] for the preparation of silica impregnated with silver nitrate involve the addition of silver nitrate solution to silica and drying the mixture under reduced pressure in a rotary evaporator.
When these procedures were repeated in our laboratory, however, there were always problems as about one-third of the adsorbent rose up the condenser of the evaporator. Therefore, the rotary evaporator had to be cleaned and reassembled and the yield of the adsorbent was only around 70%.
TLC plates coated with silica impregnated with silver ions, prepared by literature [6,7,10,11] methods have the defect that the adsorbent is not strong enough and might be destroyed by spraying agents or by heating, and all the plates must be used within 1 week as otherwise, they become dark.
We report here modified and convenient procedures for the preparation of flash columns and TLC plates using silica impregnated with silver nitrate and their application to the separation of steroids and triterpenes.