An approach is described for measuring electron self-exchange rate constants (k11) 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 TlI aquo ions in aqueous HClO4. TlIII is prepared using 203Tl-enriched Tl2O3 (203Tl abundance, ∼36%), and TlI is 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 TlI as TlBr. Isotope abundances are measured in the TlBr precipitate and TlIII solution phases using ICPMS with minimal sample preparation; an NIST 981 (common lead) spike is added, and the 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 k11 of (1.0 ± 0.1) × 10-4 M-1 s-1 was obtained in 1.5 M aqueous HClO4 at 25°C. The obtained k11 compares favorably to a value of 1.1 × 10-4 M-1 s-1 based upon a previously published study of this exchange reaction using radiolabeled (204Tl) reactants.
|Original language||English (US)|
|Number of pages||6|
|State||Published - Nov 1 1995|
ASJC Scopus subject areas
- Analytical Chemistry