Influence of Temperature on Selectivity under RP-HPLC and IPC Conditions

2 INFLUENCE OF TEMPERATURE ON SELECTIVITY UNDER RP-HPLC AND IPC CONDITIONS 

Similarly, contrasting effects of column temperature on selectivity were reported. The following section will highlight the thermodynamic signatures of these phenomena. Thermodynamic equilibrium constants at constant pressure, at variance 

Different analytes are characterized by diverse standard free energy changes (AjU°) thus the dependence of Kle and Kgo on temperature is a function of analyte nature. The following Gibbs equation relates to AH° and AS°, that represent the standard enthalpy and entropy changes, respectively  

This expression is known as the van t Hoff eqnation. It is useful because the thermodynamic enthalpy and entropy parameters for the analyte transfer from the mobile to the stationary phase may be evalnated via the effect of temperature on the thermodynamic eqnilibrinm constant. Under simple reversed phase conditions for an analyte E, Kle is snfficient to describe the system and since 

FIG U RE 10.1 Typical van t Hoff plot for different model analytes. 

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