Separation of a Mixture of Organic Acids and Their Analytical Determination

Separation of a Mixture of Organic Acids and Their Analytical Determination

The method uses ion chromatography exclusion in a continuous mode to separate and analyze a mixture of acetic acid, citric acid, lactic acid and thiodiglycolic acid (TDGA) or a mixture containing dithiodiglycolic acid (DTDGA) in addition to these acids. The arrangement used (Fig. 1) comprises in succession 1) a supply of the eluant, which is octanesulfonic acid, 2) a pump for conveying the eluant, 3) an injection valve, 4) a separator containing an ice- type resin which is penetrated only by undissociated molecules as if it were covered by a semipermeable membrane, 5) an electrochemical detector for optionally determining DTDGA and TDGA, 6) a suppressor reducing the conductivity of the eluant, and 7) a conductivity cell for determining the acids. During operation, a sample containing the acids is injected into the eluant flow and passed through the separator column, the suppressor and the conductivity detector. The retention time of the stronger acids (citric acid) in the separator is shorter than that of the weaker ones (acetic acid). In the suppressor, the H+ ions are exchanged by tetrabutylammonium ions. This exchange proceeds continuously by passing tetrabutylammonium hydroxide through the suppressor in the counterflow direction and is sufficiently effective to yield a baseline separation between all four (chromatogram, Fig. 2) and five acids, respectively (chromatogram, Fig. 3). For...