Retention studies of sulphated glycosaminoglycan disaccharides on porous graphitic carbon capillary columns

Abstract

SummaryThe retention behaviour of highly polar and charged disaccharide isomers has been studied on porous graphitic carbon columns and experimental parameters were varied over wide a range, including concentration and type of mobile phase constituents as well as temperature. The hydrophilic and anionic sugar analytes were highly retained on this stationary phase compared to the octadecyl-derivatized silica packings more commonly used. E.g., an increase in retention with polarity of a solute and with temperature was observed. By isotherm measurements and nonlinear fitting of Langmuirian expressions to the experimental data the graphite surface appeared homogeneous with only one kind of active adsorption site for these kinds of compound which was furthermore supported by the linearVan't Hoff plots obtained byvarying the temperature. The gain in free energy was found to be entropically driven after determination of the AH ~ and AS ~ values. However, enthalpy-entropy compensation behavior was not met.

Saccharose effects on surface association of phenol derivatives with porous graphitic carbon

“…(8) shows that if a plot of ln k T versus H • evaluated at a constant temperature T, is a linear function, a compensation temperature β can be therefore evaluated from the slope [20]. As Ranatunga et al have been recently demonstrated, the similarity of the values for the compensation temperature β showed only that the relative contributions of enthalpy and entropy to the overall free energy are the same in the two processes [21].…”

“…The PGC column packing has shown the remarkable ability to separate isomers or closely related compounds [5,6]. Furthermore, PGC has a high chemical and physical stability, enabling repeated use without loss of performance and reproducibility [7,8]. It is an extremely strong adsorbent [8] due to the existence of large dispersion forces between the solute and rigid planar graphite surface.…”

“…Furthermore, PGC has a high chemical and physical stability, enabling repeated use without loss of performance and reproducibility [7,8]. It is an extremely strong adsorbent [8] due to the existence of large dispersion forces between the solute and rigid planar graphite surface. PGC exhibits high retention for polar solutes mainly caused by specific interactions with the electronic structure of graphite, the retention and selectivity mechanisms are still being investigated [9][10][11].…”

Liquid chromatography analysis of monosubstituted sulfobutyl ether‐β‐cyclodextrin isomers on porous graphitic carbon

“…The exceptional retention properties of porous graphitic carbon for highly polar and charged analytes are attributable to its specific polar retention effect. The presence of both electronic competitor (acetate, formate, or hydrogen carbonate anion) and organic modifier (methanol or acetonitrile) in the mobile phase was found to be inevitable in the elution of sulfated glycosaminoglycan disaccharides [28] or sulfated oligosaccharides on PGC [29,30]. The addition of an organic modifier is necessary to regulate the strongly hydrophobic character of PGC, whereas the presence of an eluent anion is needed to compete with the anionic analytes in a process comparable to ion-exchange chromatography.…”

“…This polar retention effect makes PGC a widely accepted tool for the separation of ionisable compounds, monosaccharides, oligosaccharides, glycopeptides [25,26], and compounds that contain numerous hydroxide, carboxyl and amino groups [21,23,24]. This chromatographic support was successfully employed for the separation of structurally similar anionic carbohydrates such as glucosinolates [27], sulfated glycosaminoglycan disaccharides [28], sulfated oligosaccharides from mucin glycoproteins [29], or j-carrageenans [30], and also for the analysis of native cyclodextrins (CDs) [31] and their glucosyl derivatives [26]. The retention of native CDs on PGC is quite different from that on reversed phases as it was shown to increase with increasing molecular size like that observed with NH 2 -bonded phases [26,31].…”