New theoretical approaches to the problem of anion exchange selectivity were formulated for the example of ion-chromatographic separation of chlorine oxoanions and chloroacetic acids with various sorbents. Correlation dependences of the retention factor on the molar mass, enthalpy and entropy of hydration, ion radius, and polarizability of ions were determined.Despite the wide introduction of selective spectroscopic and mass-spectrometric detection methods into practice of ion chromatography [1, 2], steadily increasing attention has been paid to studies of the ion retention mechanism and reasons for selectivity.The separation factor α ij 1 , or relative retention (column selectivity), and resolution R s 2 of analytical signals are most important parameters of the chromatographic process [3,4]. The value of α ij is determined by thermodynamic characteristics of substances [5]; it is affected by the nature of components subjected to chromatographic analysis, and also by the type of the sorbent and composition of the eluent. However, a separation factor exceeding unity is a necessary, but not suffi cient condition for separation of mixture components, because it does not describe the quality of the separation process. The resolution R s of two chromatographic peaks takes into account not only their positions, but also peak widths. It should be noted that a wide variety of factors affects the selectivity of an anion-exchange column.It has been reported [6] the selectivity can be provided in anion exchange by optimization of such characteristics of functional groups of quaternary ammonium bases as linear dimensions, volume, and hydrophobicity of alkyl radicals. The ion-exchange selectivity was considered in [7] in terms of inner-diffusion processes. It is believed [8] that a common feature, formation of an induced cationanion pair in the sorbent phase, is inherent in various types of ion chromatography: ion exchange, ion pair, or zwitterion (electrostatic). Therefore, the selectivity is defi ned as the relative capacity of ions to form pairs of this kind. It has been shown [9] that effective separation is only possible if competitive sorption mechanisms are operative.In [10], a method of selective anion exchange capacity gradient chromatography with a borate eluent was recommended. Another way to change the concentration of functional groups is by addition of an ion pair reagent to the eluent, which diminishes the "effective" charge in the surface layer of the ion exchanger [11].The relationship between solvation processes in the mobile phase and the ion exchange separation selectivity -----------------is the reduced retention time of ions of ith and jth types, being separated; ω i and ω j , base widths of chromatographic peaks; k' = τ' R /τ 0 , retention factor; k -= (k i + k i + 1 )/2; and N, number of theoretical plates.
