摘要：

Ion exclusion, a manifestation of the Donnan effect, separates ionized from nonionized substances by excluding the former and utilizes the same ion-exchange materials as does ion exchange but at desorbing, as opposed to absorbing conditions. Ionizable substances can be partially excluded from the internal liquid of a similarly charged ion exchanger according to their degree of ionization, which can be adjusted by the pH and ionic strength of the elution solution. This principle can be applied to achieve chromatographic separations of the ionized substances, while the nonionized substances are simultaneously resolved by partition chromatography. This procedure has been studied, taking the common nucleosides as model compounds, for the influence of several separation parameters—pH, temperature, ionic strength, organic solvent, and flow rate. The results indicate that ion-exclusion chromatography is not only feasible but, with respect to "base analysis," has practical advantages (speed; dilute, volatile eluants; small plate heights; satisfactory resolutions) over comparable forms of ion-exchange chromatography. The method successfully resolves a mixture of nanomole amounts of 4-thiouridine, pseudouridine, uridine, ribothymidine, guanosine, cytidine, and adenosine in 1 hr or less and utilizes dilute, volatile eluants (0.02 m (NH 4) 2CO 3, pH 9.3 or 9.8). Optimum conditions for the separation of ribonucleosides, deoxyribonucleosides, and purine and pyrimidine bases by ion-exclusion chromatography are described.

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