Separation of C 1–C 5 aliphatic carboxylic acids on a highly sulfonated styrene–divinylbenzene copolymer resin column with a C 6 aliphatic carboxylic acid solution as the mobile phase

Abstract

Simultaneous separation of C 1–C 5 aliphatic carboxylic acids (formic, acetic, propionic, iso-butyric, butyric, iso-valeric and valeric acids) on a highly sulfonated styrene–divinylbenzene copolymer resin column (TSKgel SCX, 150 mm×6 mm i.d.) was performed with C 6 aliphatic carboxylic acids (3-methyl- n-valeric, iso-caproic and caproic acids) solutions as the mobile phases. Using 0.05 mM sulfuric acid at pH 4.0 as the mobile phase, although good separation of these C 1–C 5 acids was achieved, peaks of the C 5 acids ( iso-valeric and valeric acids) with large hydrophobicity tailed strongly. In contrast, using 1 mM C 6 acids at pH ca. 4.0 as the mobile phases, although vacant peaks corresponding to the C 6 acids in the mobile phase appeared, the peak shapes of the C 5 acids were improved greatly. Excellent simultaneous separation, symmetrical peaks and relatively high-sensitivity conductimetric detection for these C 1–C 5 acids were achieved on the TSKgel SCX column in 15 min with 1 mM iso-caproic acid at pH 4.0 as the mobile phase.