Evaluation of a C18 hybrid stationary phase using high-temperature chromatography

Alkyl benzenes and aromatic alcohols were used as model analytes in a chromatographic separation on a new type of hybrid C18 stationary phase. The stationary phase was characterized from the point of view of its interaction with the mentioned analytes. The thermodynamic parameters such as ΔH° and ΔS° showed that there are very few differences in the interactions of the alkyl benzenes and aromatic alcohols with the stationary phase in the temperature interval from 150 to 200 °C. A temperature study in the range from 30 to 200 °C using toluene as an analyte revealed that the van't Hoff plot is non-linear. Differential scanning calorimetry studies on this stationary phase indicated a phase transition at ∼90 °C. Studies on the influence of organic modifier concentrations indicated that the retention of the analytes at 150 °C varied linearly with the volume fraction of acetonitrile in the mobile phase. At 150 °C the van Deemter plot showed that a minimum was reached for the reduced plate height at ∼1.6 mL/min which was constant up to 5 mL/min. A 1-month stability study of the column using pure water as a mobile phase, at 200 °C indicated that analyte retention factor changed by 10% during this period of time.