Solvent Composition Effects in the Chromatography of Alkaloids in the Systems Water + Methanol/Silanized Silica

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Abstract
For systems of the type silanzized silica binary aquo-organic solvent, linear log k'' vs. % H2O plots are often obtained, the lines spreading fanwise in the direction of increased concentration of water. An example of such plots for a group of barbiturates barbital, heptobarbital, allobarbital, brallobarbital, cyclobarbital, hexobarbital, heptabarbital, pentobarbital and secobarbital is reported. For solutes which have more differentiated structures (especially in terms of the number and type of hydrophilic groups) less regular relationships can be obtained, as illustrated by log k'' vs. % H2O plots of 8 alkaloids [caffeine, narceine, colchicine, santonin, codeine, brucine, cinchonidine and aconitine].