Relative retention, resolution enhancement

The achievement of "ultra-high resolution conditions is a complex interaction between column efficiency, relative and absolute retention. In most cases, it is easier to increase plates if time and practical capacity are not important. Selectivity enhancement through choice of stationary phase can be a simplifying approach for difficult separations where interest is in certain critical pairs and where practical capacity is deemed Important. 

The many interactions that the solutes experience in a micellar chromatographic system enhances the differences among them. The possibility of using, simultaneously, the three most significant variables that affect the retention (j. e., pH, and concentrations of surfactant and modifier), will improve the capability of resolution of complex mixtures of ionic and nonionic compounds. The high accuracy in the prediction of retention factors in MLC permits the reliable and relatively rapid optimization of the composition of the mobile phase for the separation of a mixture of compounds, by using an interpretive method and a reduced number of mobile phases (at least two for one variable, four or five for two variables, and nine for three variables). 

The addition of organic modifiers can produce somewhat drastic effects upon the partitioning equilibria of both ions and ion pairs and hence upon the relative capacity ratio of the solute components. Variation of the concentration of 1-pentanol in chloroform as the mobile phase during the separation of alkylam-monium ions with naphthalene 2-sulfonate as the counter ion proved to be a powerful tactic in enhancing resolution (70). Increasing the ionic strength too much leads to reduced retention of the solute as the added ions compete with the solute for pairing sites (210). 

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