Separation of C1–C5 aliphatic carboxylic acids on a highly sulfonated styrene–divinylbenzene copolymer resin column with a C6 aliphatic carboxylic acid solution as the mobile phase Original Research Article

Simultaneous separation of C1–C5 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 C6 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 C1–C5 acids was achieved, peaks of the C5 acids (iso-valeric and valeric acids) with large hydrophobicity tailed strongly. In contrast, using 1 mM C6 acids at pH ca. 4.0 as the mobile phases, although vacant peaks corresponding to the C6 acids in the mobile phase appeared, the peak shapes of the C5 acids were improved greatly. Excellent simultaneous separation, symmetrical peaks and relatively high-sensitivity conductimetric detection for these C1–C5 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.