Abstract
An approach is described for measuring electron self-exchange rate constants (k 11 ) in solution based upon stable isotope-labeled reactants, chemical separations, and inductively coupled plasma mass spectrometry. The technique is demonstrated for the exchange between Tl III and Tl I aquo ions in aqueous HClO 4 . Tl III is prepared using 203 Tl-enriched Tl 2 O 3 ( 203 Tl abundance, ∼36%), and Tl I is prepared from natural abundance Tl reagents (natural 203 Tl abundance, 29.52%). The exchange is monitored by mixing the labeled and unlabeled reactants and performing timewise separations through selective precipitation of Tl I as TlBr. Isotope abundances are measured in the TlBr precipitate and Tl III solution phases using ICPMS with minimal sample preparation ; an NIST 981 (common lead) spike is added, and the 208 Pb/ 206 Pb is measured as an internal standard to correct for mass discrimination. The self-exchange rate constant is determined from a McKay plot obtained from the 205 Tl abundances of either oxidation state. A k 11 of (1.0 ± 0.1) x 10 -4 M -1 s -1 was obtained in 1.5 M aqueous HClO 4 at 25 °C.
Published Version
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