Automated programmable pressurized carbonic acid eluent ion exclusion chromatography of organic acids

Conductometric ion exclusion chromatography of weak acids does not enjoy the same degree of success as its counterpart in suppressed conductometric anion exchange chromatography. Compared to the latter, eluent preparation is not automated. Commonly, a strong acid is used as the eluent leading to a relatively high-detector background and poorer limits of detection. In addition, generally applicable gradient elution has not been possible. We introduce the automated preparation of carbonic acid eluents at concentrations exceeding 0.15 M by introducing CO2 into a flowing water stream through the walls of a Teflon AF® capillary tube under pressure; the resulting eluent concentration is controlled by varying the CO2 pressure in a programmed manner. The acidic carbonic acid solution functions as the eluent and can be almost completely removed (detector background 1.2-1.6 μS/cm) by an improved carbon dioxide removal device before detection. Theoretical and practical considerations are discussed and illustrative isocratic and gradient ion exclusion chromatography is demonstrated.