## Thermodynamic Characterization for the Convergence Coordinates of Molecular Structure Parameters of Homologues in Reversed-Phase High Performance Liquid Chromatography

**ZHANG Jing, WANG Yan, GENG Xin du (Institute of Modern Separation Science,Northwest University, the Key Laboratory of Mondern Separation in Shanxi Province,Xi′an,710069)**

According to stoichiometric displacement model for retention(SDM R),the covergent phenomenon of molecurlar structure parameters of homologues in reverse phase liquid chromatography (RPLC) was characterized by thermodynamical function.A general equation for calculating the coordinates of the convergent point was derived and the physical meanings of the coordinates were elucidated from the standpoint of view of thermodynamics.Because any constant times RT ( R is gas constant, T is absolute temperature) to have energy unit,the ordinate of all the convergence has the same free energy change to equal the free energy change of the column phase ratio.The abscissca is compensate free energy for that from Z and these molecular stucture parameters.It was further discussed the reason why the essence of the convergence of homologues is the total free energy change being zero.The derived equation was tested with experiment and reference′s data and found that these data fit the expected result very well.

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