Abstract
Ionized organic compounds can be extracted into organic phases as ion-pairs with counter ions of suitable hydrophobic character. The distribution ratio depends on the structure of the ion-pair and the concentration of the counter ion. Systems for liquid—liquid partition chromatography are easy to adapt to different types of compounds and have a high selectivity. The counter ion is selected on the basis of batch extraction procedures or chromatographic tests. A photometric detector can be used for samples of <0.1 nmole of non-absorbing compounds if a counter ion with high absorbance is used. Straight-phase systems with a high counter-ion concentration on a cellulose support have a high sample capacity and good separating efficiency ( H ⩽ 0.5 mm at a mobile phase speed of ⩽ 3 mm/sec when k′ ⩾ 5). Examples are given of straight-phase separations of carboxylic acids with a quaternary ammonium ion as counter ion in the stationary phase and amines and quaternary ammonium ions with picrate or β-naphthalene sulphonate as counter ions. Aminophenols have been separated by reversed-phase systems containing bis-(2-ethylhexyl)phosphoric acid in chloroform as the stationary phase.
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