Rapid communications in mass spectrometry : RCM · 2026
Exploratory Measurements of Singly Substituted and Clumped Isotopologues in Iodate Using Electrospray Ionization Mass Spectrometry.
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Lucarelli Jamie, Bubas Amanda R, Cox Richard M, Lehmann Sophie B, Tripati Aradhna, Engelmann Mark, Conte Elise R
Аннотация
RATIONALE: Clumped isotope geochemistry can reveal the temperatures and chemical pathways at which molecules form, but it remains unexplored for most inorganic systems. Iodate (IO3 -) is central to ocean and atmospheric iodine cycling and to tracking radioactive iodine from nuclear activity. Here, we report the first exploratory investigation into the feasibility of measuring bulk and clumped isotopologues in iodate using electrospray ionization mass spectrometry (ESI-MS).
METHODS: Sodium iodate was dissolved in either deionized water or 97% H2 18O. Two sample sets systematically varied the H2 18O fraction of the spray solvent from 0% to 97%. Samples were infused into a Thermo Scientific TSQ Quantum Access MAX triple-quadrupole mass spectrometer with an atmospheric pressure ionization source operated in negative-ion scan mode. Spectra were acquired over m/z 110-190 and averaged across 25 scans.
RESULTS: The singly substituted isotopologue (127I16O2 18O-, m/z 177), clumped isotopologues (127I16O18O2 -, m/z 179; 127I18O3 -, m/z 181), and isotopologue distributions were resolved in IO3 -. Relative isotopologue abundances shifted monotonically with solvent 18O content; 127I18O3 - increased from 0% to 56% across the enrichment range. In the natural abundance sample, measured isotopologue abundances matched the values predicted for a stochastic (random) isotope distribution, confirming that the instrument is sampling the natural isotopologue distribution without significant bias. We also report isotopologue distributions for IO- and IO2 -, which exhibit isotopic trends similar to those observed for IO3 -.
CONCLUSIONS: These first measurements of isotopologues in IO3 - establish ESI-MS as an accessible platform for isotopic analysis of inorganic oxyanions under enriched conditions. We discuss the thermodynamic basis for equilibrium clumping in IO3 -, the analytical requirements for extending these enriched sample measurements to natural abundance clumped isotope thermometry, and the potential applications of this system in Earth and nuclear sciences.
METHODS: Sodium iodate was dissolved in either deionized water or 97% H2 18O. Two sample sets systematically varied the H2 18O fraction of the spray solvent from 0% to 97%. Samples were infused into a Thermo Scientific TSQ Quantum Access MAX triple-quadrupole mass spectrometer with an atmospheric pressure ionization source operated in negative-ion scan mode. Spectra were acquired over m/z 110-190 and averaged across 25 scans.
RESULTS: The singly substituted isotopologue (127I16O2 18O-, m/z 177), clumped isotopologues (127I16O18O2 -, m/z 179; 127I18O3 -, m/z 181), and isotopologue distributions were resolved in IO3 -. Relative isotopologue abundances shifted monotonically with solvent 18O content; 127I18O3 - increased from 0% to 56% across the enrichment range. In the natural abundance sample, measured isotopologue abundances matched the values predicted for a stochastic (random) isotope distribution, confirming that the instrument is sampling the natural isotopologue distribution without significant bias. We also report isotopologue distributions for IO- and IO2 -, which exhibit isotopic trends similar to those observed for IO3 -.
CONCLUSIONS: These first measurements of isotopologues in IO3 - establish ESI-MS as an accessible platform for isotopic analysis of inorganic oxyanions under enriched conditions. We discuss the thermodynamic basis for equilibrium clumping in IO3 -, the analytical requirements for extending these enriched sample measurements to natural abundance clumped isotope thermometry, and the potential applications of this system in Earth and nuclear sciences.