Abstract
A strategy is described for rapid on-line measurement of electron self-exchange rates between aqueous FeIII and FeII in aqueous solution using stable 57Fe-labeled reactants, cation chromatography, and inductively coupled plasma mass spectrometry. The self-exchange is monitored by mixing the reactants and performing timewise separations of FeII and FeIII ions. Separations are completed in 30−60 s using a weak phosphonic/carboxylic acid cation exchange guard column and 0.1−0.5 M aqueous HClO4 eluent. The resulting time series of 56Fe and 57Fe chromatograms display systematic changes in isotopic abundances from which the self-exchange rate constant, k11, is obtained. Two different schemes are used for mixing and sampling the reaction mixture; using a peristaltically pumped flow reactor, reaction half-lives on the order of 30 s can be monitored. A series of k11 results are obtained under a variety of temperature (2.0, 21.6, and 25.0 °C) and ionic strength conditions (0.10, 0.50, and 0.55 M aqueous HClO4) which are congruent with three previously published radiolabeling studies for this reaction.
Published Version
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