An approach is described for measuring electron selfexchange rate constants (An) in solution based upon stable isotope-labeled reactants, chemical separations, and inductively coupled plasma mass spectrometry. The technique is demonstrated for the exchange between TlIII and Tl1 liaquo ions in aqueous HClO4. TlIIIis prepared using 203Tl-enriched Tl2O3(203Tl abundance, ~36%), and TlIis prepared from natural abundance Tl reagents (natural 203Tl abundance, 29.52%). The exchange is monitored by mixing the labeled and unlabeled reactants and performing timewise separations through selective precipitation of 11 as TlBr. Isotope abundances are measured in the TlBr precipitate and solution phases using ICPMS with minimal sample preparation; an NIST 981 (common lead) spike is added, and tibe 208Pb/206Pb 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 205Tl abundances of either oxidation state. A An of (1.0 ± 0.1)×10 4 M-1s-1was obtained in 1.5 M aqueous HClO4at 25 °C. The obtained An compares favorably to a value of 1.1×10-4 M-1s-1based upon a previously published study of this exchange reaction using radiolabeled (204 ) reactants.
ASJC Scopus subject areas
- Analytical Chemistry