Journal
JOURNAL OF CHROMATOGRAPHY A
Volume 1217, Issue 39, Pages 6092-6096Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.chroma.2010.07.059
Keywords
Porous graphitic carbon; Temperature; Organic modifier; Malto-oligosaccharides; van't-Hoff Plots
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Porous graphitic carbon (PGC) is known as well suited adsorbent for liquid chromatography of carbohydrates. In this work we report on systematic investigations of solvent effects on the retention mechanism of fluorescence labeled malto-oligosaccharides on PGC. The adsorption mechanism was found to depend on the type of organic modifier used in the mobile phase. Positive adsorption enthalpies and entropies, which have already been reported in the literature, were solely produced using acetonitrile. Both alternative solvents (tetrahydrofuran, 2-propanol) yielded in contrast negative enthalpies. As plausible retention mechanism for oligosaccharides on PGC applying acetonitrile as mobile phase component we propose the formation of a dense and highly ordered solvation layer of the PGC surface with the linear acetonitrile molecules. Adsorption of analyte molecules requires a displacement of numerous acetonitrile molecules, which explains the positive enthalpy and entropy values measured. The interplay of enthalpic and entropic contributions to the overall adsorption phenomena results in strongly temperature dependent chromatographic selectivity values. (C) 2010 Elsevier B.V. All rights reserved.
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