Although pH Zone Refining was introduced 20 years ago by Yochiro Ito, it finds little use as a separation method in the separation of natural products or synthetic compounds, with less than 100 articles, to date, describing its use.  This, despite the fact, that it gives very fine separations and allows unusually high loadings, which are beyond normal CCC capacities and much higher than solid phase LC techniques. Simply thought of a liquid-liquid ion exchange chromatography, pH Zone Refining relies on the large difference in partition coefficients in aqueous systems between the ionized and unionized forms of the same analyte.  Thus by modeling the stationary and mobile phases such that the pH of the eluent will pass through the dissociation constant of the desired analyte one can effect a situation where the distribution coefficient of the analyte suddenly changes from strongly favoring the stationary phase to strongly favoring the mobile phase.  The result being that the analyte is eluted, not as a typical Gaussian distribution curve, but as a sharp rectangular peak of high concentration.  The method is applicable to any ionizable compound stable in both the ionic and neutral forms, including alkaloids, carboxylic and other acids including phenols.  Examples of each of these classes will be presented.

pH Zone  refining: An underused mode of an underutilized technology with enormous potential for difficult separations

246th National Meeting (2013)

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