Superheated water chromatography on phenyl bonded hybrid stationary phases

Phenyl bonded XTerra and XBridge organic/inorganic hybrid stationary phases have been used to separate test solutes and phenol homologues with a pure water mobile phase over a temperature range from 40 to 200 degrees C. The van't Hoff relationships between retention factors and reciprocal temperature were non-linear and could either be interpreted as a systematic change in the properties of the XTerra phenyl column or a marked change in the phase material for the XBridge phenyl column. This was reflected in the methylene selectivity which also showed a change for the XBridge column. The changes in column efficiencies and optimum flow rates were also examined and these suggested that at high temperatures the diffusion of the analytes was significant.