920 (2001) 87–93 Journal of Chromatography A, www.elsevier.com / locate / chroma Novel stationary phase with regulated anion-exchange capacity Maria G. Kiseleva, Pavel N. Nesterenko* Division of Analytical Chemistry, Lomonosov Moscow State University, Vorob’ evy Gory GSP-3, Moscow 119899, Russian Federation Abstract A novel stationary phase — phenylaminopropyl (PLA) bonded silica — is proposed for anion-exchange chromatography. Low basicity (pK about 2.5) attached to silica phenylaminopropyl groups allows a variation of surface density of protonated a sites in the pH range from 2 to 5. This enables us to use the same column for the separation of anions having different affinity to anion-exchangers. The effect of mobile phase pH on conditional capacity of PhA-silica was studied. The hypothesis on dependence of ion-exchange selectivity on the column capacity is discussed. Suitability of PhA-silica for ion-chromatographic separation of organic and inorganic anions at different pH values of eluent was demonstrated.  2001 Elsevier Science B.V. All rights reserved. Keywords: Stationary phases, LC; Ion-exchange chromatography; Phenylaminopropylsilica stationary phases; Selectivity; Silica, phenylaminopropyl; Inorganic anions 1. Introduction capacities and a few commercially available columns with specified properties. As a rule, the retention of anions in ion chroma- A new approach to optimization of the column tography (IC) is dependent on the nature / charge of capacity — capacity gradient ion chromatography — the eluent and can be additionally regulated by was proposed recently by Yamamoto et al. [2]. This change of concentration or pH, or can be varied with method is based on the ability of hydroxyl residues column temperature changes. Less attention has been at the resin surface to form complexes with attached paid to a possibility of variation of the retention by amino groups, thus reducing conditional anion-ex- change of the ion-exchange capacity of ion ex- change capacity. At the beginning of the analysis, changers. Usually the anion-exchange capacity is hydroxyl residuals are blocked in the complexes with defined at the stage of stationary phase synthesis. As dihydroxyphenylborane added to the eluent. Gradual in the case of anion exchangers, the item functional increase of eluent pH causes their dissociation, groups are quaternary ammonium [1], the ion-ex- increasing interaction between hydroxyl residues and change capacity of a particular phase is constant. To bonded amino groups and thus forces decrease of achieve the separation of different anions the analyst resin’s conditional anion-exchange capacity. Thus should have a set of anion exchangers with different the capacity gradient IC allows the efficient sepa- ration of anions with very different affinity to the anion exchanger. *Corresponding author. Analytical Chemistry Division, Depart- The anion-exchange capacity manipulation can be ment of Chemistry, M.V. Lomonosov Moscow State University, also accomplished by a simple change in protonation Lenin Hills, Moscow 109028, Russian Federation. Tel.: 17-095- degree of primary, secondary or tertiary amino 939-4416; fax: 17-095-939-4675. E-mail address: paveln@analyt.chem.msu.ru (P.N. Nesterenko). groups in case of a weak anion exchanger. However, 0021-9673 / 01 / $ – see front matter  2001 Elsevier Science B.V. All rights reserved. PII: S0021-9673(01)00694-X