[Study on the rule of solvent strength in reversed-phase liquid chromatography]

Based on the physical meanings of Z (total moles of the released solvent at the contact region between solute and stationary phase), and j(the slope of the linear plot of lg I versus Z, a constant relating to the affinity of organic solvent to the stationary phase) of stoichiometric displacement model for retention (SDM-R) of solute in liquid chromatography(LC), both Z and j could be employed to characterize solvents, therefore, Z value only can be used as a characterization parameter for fixed solute and stationary phase. However, the parameter j is independent of solutes. As long as phase is given, j can be employed as a new characterization parameter of organic solvent strength in LC. With the homologues of methanol, ethanol and n-propanol as organic solvents in mobile phase and n-alkylalcohols as solutes, both the SDM-R and Snyder's empirical equation were tested, and compared with the corresponding parameters obtained from Snyder's empirical equation. With S [the slope of the linear plot of lg k' (k' is capacity factor) vs psi(volume fraction of organic solvent in mobile phase)] and lg kw0(the intercept of this plot), it was found that the two linear plots with the SDM-R, lg k' vs the composition of mobile phase and lg I vs Z were better than the corresponding plots with Snyder's empirical equation. The results indicate that Z, lg I and j decrease with the increase in the molecular size of the organic solvent of the homologue. This fact indicates that the solvent strength in LC depends on the size of solvent molecules. And the greater the solvent molecules, the stronger the solvent strength is. Furthermore the solvent strength was found to follow homologous rule. The j value may become a new parameter for the characterization of organic solvent strength in LC.