Eluents for ion-exclusion chromatography

For the separation of organic acids, mineral acids and long-chain aliphatic carboxylic acids are usually employed as eluents. Among mineral acids, hydrochloric acid and sulfuric acid are the most commonly used. When applying direct UV detection, stdftu ic acid is usually used as an eluent [4,8], while hydrochloric acid 

A common characteristic of all polystyrene/divinylbenzene-based ion-exclusion phases is the high retention of aromatic carboxylic acids. This is due to 7t-7t interactions between the aromatic ring systems of the polymer and the solute. The separation of aromatic carboxylic acids, therefore, is more elegantly accomplished by the various procedures of reversed-phase chromatography. 

The high retention of aliphatic monocarboxylic acids ( c 4) and aromatic carboxylic acids can be reduced by adding small amounts of an organic solvent (10 to 30 mL/L) to the eluent. This blocks adsorption sites on the surface of the stationary phase [8]. Particularly suited are acetonitrile, 2-propanol, or ethanol. If possible, methanol 

According to Tanaka and Fritz [9], comparably low background conductivities were obtained with benzoic acid as the eluent, because benzoic acid is only partly dissociated. However, the acid strength of a dilute benzoic acid solution is sufficient to elute aliphatic carboxylic acids with a good peak shape. 

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