Abstract: The analysis of seven aliphatic carboxylic acids, formic, acetic, propionic, iso-butyric, n-butyric, iso-valeric and n-valeric acids in anaerobic digestion process waters for biogas production was examined by ion-exclusion chromatography using dilute acidic eluents (benzoic acid, perfluorobutyric acid (PFBA) and sulfuric acid) and non-suppressed conductivity / UV detection. The columns used were a styrene/divinylbenzene-based strongly acidic cation-exchange resin column (TSKgel SCX) and a polymethacrylate-based weakly acidic cation-exchange resin column (TSKgel Super IC-A/C). A good separation was performed on the TSKgel SCX in shorter retention times. For the TSKgel Super IC-A/C, peak shape of the acids was sharp and symmetrical in spite of longer retention times and the mutual separation of the acids was good except for iso- and n-butyric acids. The better separation and good detection was achieved by using the two columns (TSKgel SCX and TSKgel Super IC-A/C connected in series), lower PFBA and sulfuric acid as eluents, and non-suppressed conductivity detection and UV detection at 210 nm, and was applied to anaerobic digestion process waters. The chromatograms with conductivity detection were relatively simple compared to those with UV detection. The use of two columns with different selectivity for aliphatic carboxylic acids and two detection modes was effective for determination and identification of the analytes in anaerobic digestion process waters containing complex matrices.

Key words: aliphatic carboxylic acids, anaerobic digestion process waters, ion-exclusion chromatography, non-suppressed conductivity and UV detection, perfluorobutyric and sulfuric acids eluents, strongly and weakly acidic cation-exchange resin columns