ION-EXCLUSION CHROMATOGRAPHY WITH CONDUCTIMETRIC DETECTION OF ALIPHATIC CARBOXYLIC-ACIDS ON AN H+-FORM CATION-EXCHANGE RESIN COLUMN BY ELUTION WITH POLYOLS AND SUGARS

The Ion-exclusion chromatography (IEC) of normal aliphatic carboxylic acids of different acidity (pK(a)) and hydrophobicity was investigated on a poly(styrene-divinylbenzene) (PS-DVB)-based strongly acidic cation-exchange resin column in the H+ form and conductimetric detection. When water was used as the eluent, although the C-1-C-5 carboxylic acids were separated from strong acid (HCl) depending on the pK(a) and the hydrophobicity, the resolution was low and the peaks were accompanied by leading depending on their hydrophobicities. To improve the peak shape and the peak resolution, aqueous eluents of polyols and sugars containing 1-8 alcoholic OH groups (methanol, ethylene glycol, glycerol, erythritol, xylitol, fructose, sorbitol, and sucrose) were tested for the IEC separation of the carboxylic acids. When aqueous eluents of polyols and sugars were used, the tendency for leading peaks was decreased drastically with increasing number of OH groups in the polyols and sugars. This is due mainly to the increase in the the hydrophilicity of the PS-DVB surface by the OH groups. An aqueous eluent of 10% methanol-0.15 M sucrose gave a reasonable resolution and highly sensitive detection for carboxylic acids. This eluent has a much lower background conductivity (ca. 4 mu S cm(-1)) and much higher detection sensitivity (ca. 170 times higher for valeric acid) than the 0.5 mM sulfuric acid (ca. 390 mu S cm(-1)) commonly used as an eluent in conventional IEC with conductimetric detection.