MEASUREMENT OF TL(III/I) ELECTRON SELF EXCHANGE RATES USING ENRICHED STABLE ISOTOPE LABELS AND INDUCTIVELY COUPLED PLASMA MASS SPECTROMETRY

摘要

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 T1(III) and T1(I) aquo ions in aqueous HClO4. T1(III) is prepared using (203)T1-enriched T1(2)O(3) ((203)T1 abundance, similar to 36%), and T1(I) is prepared from natural abundance T1 reagents (natural (203)T1 abundance, 29.52%). The exchange is monitored by mixing the labeled and unlabeled reactants and performing timewise separations through selective precipitation of T1(I) as T1Br, Isotope abundances are measured in the T1Br precipitate and T1(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 205T1 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 HClO4 at 25 degrees C, The obtained k(11) compares favorably to a value of 1.1 x 10(-4) M(-1) s(-1) based upon a previously published study of this exchange reaction using radiolabeled ((204)T1) reactants. [References: 32]