Abstract
A new type of thin-layer chromatography (vapor pre-adsorption TLC) in which a silica gel thin-layer pre-adsorbing the vapor of organic solvent is used as the stationary phase and a non-polar organic solvent as a developer has been presented.
Sample: 2, 4-dinitrophenylhydrazones of aliphatic aldehydes. Solvent for pre-adsorption : acetone, benzene, carbon tetrachloride, ethyl acetate. ethanol etc. Solvent for development : n-hexane, cyclohexane and petroleum ether.
A 500 ml round-bottomed flask containing 50 ml of pre-adsorption solvent is placed in a thermostat and a stream of nitrogen is introduced. The evaporated vapor of the solvent is introduced to the developing chamber and is pre-adsorbed on the surface of the thin-layer. After 1530 minutes, the developing solvent is made to flow through the layer descendingly.
As an increase in the flow volume (flow rate×time) gives larger Rf values, desired Rf values for the separation of various substances are obtained by the experimental conditions.
It is generally believed that the Rf value of a substance depends on two factors, i. e., (1) adsorptivity of the layer and (2) eluting power of the developing solvent. The author's experimental data shows that the third factor, the effect of pre-adsorption of vapor, is critically important to decide the Rf value.
