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Gradient Elution in Aqueous Normal-Phase Liquid Chromatography on Hydrosilated Silica-Based Stationary Phases
Authors: Soukup Jan | Janás Petr | Jandera Pavel
Year: 2013
Type of publication: článek v odborném periodiku
Name of source: Journal of Chromatography A
Publisher name: Elsevier Science BV
Place: Amsterdam
Page from-to: 111-118
Titles:
Language Name Abstract Keywords
cze Gradientová eluce v chromatografii s normálními fázemi na hydrosilovaných stacionárních fázích Byl studován teoretický model pro předpověď retenčních časů fenolických kyselin na hydrosilovaných stacionárních fázích. Aktuální gradient vodné složky v acetonitrilu může kolísat od přednastaveného programu, protože i gradientový acetonitril obsahuje trochu vody. Z tohoto důvodu je aktuální koncnetrace vody během gradientu vyšší než v nastaveném programu, což vede k nižším retenčním časům. Dále může být aktuální gradientový profil ovlivněn zvýšením naadsorbované vody na stacionární fázi během gradientu. Tyto vlivy byly testovány pomocí frontální analýzy a titrace dle Karl-Fischera. hydrosilovaný silikagel; chromatografie s vodně-organickými normálními fázemi; adsorpce vody; fenolické kyseliny; gradientová eluce
eng Gradient Elution in Aqueous Normal-Phase Liquid Chromatography on Hydrosilated Silica-Based Stationary Phases The possibility of applying a theoretical model in the prediction of the retention of phenolic acids on hydrosilated silica, in aqueous normal phase mode was studied. The actual gradient of the aqueous component in acetonitrile may fluctuate from the pre-set program, as even the gradient-grade acetonitrile contains some water. Hence, the actual concentration of water during the gradient run is higher than pre-set by the gradient program, which leads to lower than expected sample retention. Furthermore, the actual gradient profile may be affected by an increase in water uptake on a polar column during the gradient run. These effects were investigated using the using frontal analysis method and Karl-Fischer titration, for the determination of water in the initial mobile phase, and in the column effluent. Preferential adsorption of water on the Silica hydride, Diamond hydride, UDC Cholesterol, Bidentate C-18, and Phenyl hydride columns can be described by Langmuir isotherms. At the column saturation capacity, less than one monomolecular water layer is adsorbed, with a further decrease in coverage density for modified materials. Parameters of semi-logarithmic and logarithmic model equations, describing the dependence of retention factor on the concentration of water, were determined under isocratic conditions. These parameters and linear gradient profiles corrected for the actual water concentrations were used in calculation of gradient retention data. The corrections for the actual water concentration greatly improved the agreement between the experiment and the predicted gradient elution volumes. Generally, the semi-logarithmic model provides slightly better prediction of the gradient data, with respect to the logarithmic retention model. hydrosilated silica; aqueous normal-phase liquid chromatography; adsorption of water; phenolic acids; gradient-elution

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