Indirect photometric detection of aliphatic acids separated by ion-exclusion chromatography using aromatic acidic eluents

The use of aromatic acids as eluents for the indirect photometric detection of aliphatic acids in ion-exclusion chromatography is described. A range of aromatic acids (benzoic, salicylic, phthalic, trimesic and pyromellitic acids) were investigated to obtain optimal conditions of separation and detection as well as to obtain symmetrical peaks. Phthalic acid was the best compromise among the possible eluents. A theoretical treatment predicts a linear response of peak height to solute concentration. The peak height should also be proportional to the solute dissociation constant and inversely proportional to the dissociation constant and concentration of aromatic acids used as modifiers. These predictions were confirmed experimentally. A linear response was obtained over range of concentrations 0.1-10 mM in 1 mM phthalic acid. The proposed method was demonstrated for use in the analysis of aliphatic acids in extracts of agricultural and Australian native plants. (C) 1998 Elsevier Science B.V. All rights reserved.