The retention behavior of Br/sup -/, NO/sub 3//sup -/, Cl/sup -/, SO/sub 4//sup 2 -/, and S/sub 2/O/sub 3//sup 2 -/ in nonsuppressed ion chromatography is studied as a function of changing eluent composition. Three models, multiple species eluent, single species eluent, and single interaction sites, are utilized to predict chromatographic behavior. While all three are based on a thermodynamic equilibrium consideration of the ion exchange process, they differ in their characterization of the analyte/eluent competition or the ion/resin interaction. Despite this difference in approach, all three models effectively characterize the behavior of the analytes under elution conditions which are of practical importance. The relative utility of each model is discussed. 17 references, 4 tables.