Ion Pairing Chromatography

The present state of ion-pair chromatography (IPC) is reviewed. Emphasis is placed on the theoretical modeling of the retention behavior of charged, zwitterionic, and neutral solutes, since the theory provides the generally good understanding of the factors affecting the separation. Although stoichiometric models were credited with the first easy-to-understand demonstration of the retention mechanism of IPC, they were thermodynamic models, consistent with fundamental physics, that extensively detailed the multiplicity of interactions involved in an IPC system. This review is also aimed at giving a broad outline of the progression of the application of this technique during the past decade. Many examples will be given of the analysis of a wide variety of materials, including chiral compounds. They assess the practical potential of this separation strategy. Detection and hyphenation are also described. The relation of IPC to other instrumental method of analysis, the importance of ion-pairing in different (non-extractive) analytical techniques, and not separative aims of IPC, that are topics for which there is a dearth in the literature, are critically reviewed.