ROLE OF BARIUM IONS IN THE ANION-EXCHANGE CHROMATOGRAPHIC SEPARATION OF CARBOHYDRATES WITH PULSED AMPEROMETRIC DETECTION

Barium ion is shown here as an effective component of alkaline mobile phases for improving the separation of carbohydrates in anion-exchange chromatography with pulsed amperometric detection. We demonstrate that the introduction of barium ensures a complete removal of carbonate, making it possible to carry out a large number of separations without column reequilibration after each run. This is particularly helpful when diluted alkaline eluents (i.e., <20 mM NaOH) are employed. Under such experimental conditions, the analysis time of carbohydrates is drastically reduced and the reproducibility of the chromatographic data greatly improved. For example, the normalized capacity factor (k¢/k¢0) of lactulose, which represents the most retained compound investigated using 16 mM NaOH as the eluent, exhibits only a slight decrease from 1.00 to 0.94 after 7.5 h of chromatographic run. The net improvement in the peak shape of D-ribose, D-allose, and D-talose has been interpreted by considering the complex formation between barium and sugar molecules having an axial-equatorial-axial sequence of three OH groups on the six-membered ring. The presence of Ba(II) (0.5-0.7 mM) in alkaline eluents has been demonstrated by ion chromatography with conductivity detection.