title: Diffusion and partitioning of cations in an agarose hydrogel.
abstract: Self- and mutual diffusion were measured in a low-melt 1.5% agarose hydrogel as a function of ionic strength (0.1-100 mM) and pH (3-7) for Cd(2+) and a charged rhodamine derivative. Self-diffusion was measured by fluorescence correlation spectroscopy, whereas mutual diffusion was evaluated using a diffusion cell. In contrast to the results observed for the diffusion cell, self-diffusion of rhodamine 6G increased from 50 to 90% of that found in water as the ionic strength increased from 0.1 to 100 mM (pH = 6). The combined observations of decreasing diffusive flux in parallel with an increasing diffusion coefficient were attributed to the gel's Donnan potential. Donnan potentials obtained voltammetrically using a Au amalgam microelectrode varied from -30 to 0 mV as the ionic strength increased from 0.1 to 100 mM (pH = 6). At the low ionic strengths, Donnan potentials of this magnitude accounted for a 13× enhancement of Cd(2+) concentrations in the hydrogel, which was consistent with measurements obtained by a nitric acid extraction of the gel (15×) and able to explain the apparent discrepancy between mutual and self-diffusion measurements. The overall diffusion of the positively charged substrates decreased as the pH was decreased from 12 to 3.
authors.affiliation: Department of Chemistry, University of Montreal, P.O. Box 6128, Succursale Centre-ville, Montréal, Québec, Canada, H3C 3J7.
authors.forename: Mahmood
authors.initials: M
authors.lastname: Golmohamadi
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Davis
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Wilkinson
mesh_terms: D002104:Cadmium / Q000737:chemistry*; D002412:Cations / Q000737:chemistry; D004058:Diffusion; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D009994:Osmolar Concentration; D012685:Sepharose / Q000737:chemistry*
chemical_list: D002412:Cations; D002104:Cadmium; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate; D012685:Sepharose