The Influence of Column Temperature on the Extrapolated Values of the Retention Factor in Reversed-Phase Liquid Chromatography for Water as Mobile Phase

Abstract

The dependences of the retention factor for some aromatic hydrocarbons at different column temperatures on the concentration of the organic modifier in mobile phase (acetonitrile) were studied under reversed-phase liquid chromatography, using two C18 chromatographic columns with the same constructive characteristics. From these dependences the extrapolated values of the retention factor for the aromatic hydrocarbons were calculated and then they were used for studying their temperature dependence by means of the van't Hoff plots. The graphs between the logarithm of the retention factor and the inverse value of absolute temperature of the column were characterized by good determination coefficients. The standard enthalpy variation associated to the transfer of studied hydrocarbons from the aqueous mobile phase to the stationary phase was calculated from these van't Hoff plots.

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“…The enthalpy values derived decreased as the polarity of the mobile phase (water content) decreased, which could indicate the existence of strong specific (secondary) interaction between analytes and functional groups of the stationary phase. Calculated negative standard enthalpy changes were from −0.1 ( φ = 0.3) to −17 kJ/mol ( φ = 0.1); so they were maximized (in absolute values) at higher water content, where they exceeded −10 kJ/mol, which is a value typically observed in reversed-phase chromatography [ 59 ].…”