Effect of Temperature on the Orientation of Bonded Hydrocarbon Phases in Totally Aqueous Liquid Chromatographic Systems

Using a totally aqueous mobile phase and surfaces with chemically attached midrange hydrocarbons, unique changes in solute retention were observed as a function of increasing temperature. Initially, the In of the capacity factor decreased linearly; however, at higher temperatures a gradual sigmoidal drop in In k’ occurred. Although similar trends were seen for each surface, the magnitude and position of the resulting changes were dependent upon the amount and the length of the bonded hydrocarbon moieties, respectively. Changes in the on-set temperature for the nonlinear retention behavior were approximately 10°C per addition of each methylene group, which extended the chain length of the bonded moieties.