Thermodynamic and Kinetic Characterization of Porous Graphitic Carbon in Reversed‐Phase Liquid Chromatography

Chromatographic Assessment of Organic Compounds Using Carbon Nanotubes: The Relationship between Affinity and Dispersibility

The affinity between carbon nanotubes (CNTs) and organic compounds is of substantial importance since it strongly relates to the dispersibility of CNTs in those compounds. Several affinity evaluation methods have been developed so far, and the concept of the Hansen solubility parameter is a representative method widely used in the field of nanocarbon materials. Here, we demonstrate that CNT-loaded silica columns can effectively assess the affinity of organic compounds for CNT surface by exploiting the chromatographic retention time as a criterion. Obtained trends of the affinity of organic compounds for CNT were compared to those based on Hansen solubility parameter distance values. Most organic compounds showed similar trends, but one exceptional compound was observed. Simple CNT dispersion tests were conducted with these organic compounds to demonstrate the advantage of the chromatographic assessment. Further, we conducted comparison experiments using a pyrene-functionalized column and other CNT-loaded columns to elucidate the characteristics of each CNT column. The chromatographic approaches using CNT columns would be beneficial for realizing CNT suspensions with improved CNT dispersibility.

Solvent effects on the retention of oligosaccharides in porous graphitic carbon liquid chromatography

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.