Characterization of cross-linked cellulosic ion-exchange adsorbents: 1. Structural properties

• We examine the structural characteristics of cellulosic ion-exchange adsorbents.
• Inverse size exclusion was used to estimate the pore size distribution.
• Pore space in HyperCel is comparable to that in a polymer-modified adsorbent.
• Electron microscopy imaging was used to qualitatively assess the pore structure.
• Functional characterization of the Donnan equilibrium showed salt exclusion.

The structural characteristics of the HyperCel family of cellulosic ion-exchange materials (Pall Corporation) were assessed using methods to gauge the pore dimensions and the effect of ionic strength on intraparticle architecture. Inverse size exclusion chromatography (ISEC) was applied to the S and STAR AX HyperCel derivatives. The theoretical analysis yielded an average pore radius for each material of about 5 nm, with a particularly narrow pore-size distribution. Electron microscopy techniques were used to visualize the particle structure and relate it to macroscopic experimental data. Microscopy of Q and STAR AX HyperCel anion exchangers presented some qualitative differences in pore structure that can be attributed to the derivatization using conventional quaternary ammonium and salt-tolerant ligands, respectively. Finally, the effect of ionic strength was studied through the use of salt breakthrough experiments to determine to what extent Donnan exclusion plays a role in restricting the accessible pore volume for small ions. It was determined that Donnan effects were prevalent at total ionic strengths (TIS) less than 150 mM, suggesting the presence of a ligand-containing partitioning volume within the pore space.