A Soft Evaporation and Ionization Technique for Mass Spectrometric Analysis and Bio-Imaging of Metal Ions in Plants Based on Metal–Iodide Cluster Ionization

Abstract

Protonation/deprotonation is the well-recognized mass spectrometric mechanism in matrix-assisted laser desorption ionization of organic molecules but not for metal ions with different oxidation states. We describe herein a soft evaporation and ionization technique for metal ions based on iodination/de-iodination in metal–iodide cluster ionization (MICI). It is not only able to determine identities and oxidation states of metal ions but also reveal spatial distributions and isotope ratios in response to physiological or environmental changes. A long chain alcohol 1-tetradecanol with no functional groups that can absorb laser irradiation was used to cover and prevent samples from direct laser ablation. Upon the irradiation of the third harmonic Nd3+:YAG (355 nm, 3 ns), iohexol containing three covalently bonded iodine atoms instantly generates negative iodide ions that can quantitatively form clusters with at least 14 essential metal ions present in plants. The detection limits vary with different metal ions down to low fmol. MICI eliminates the atomization process that obscures metal charges in inductively coupled plasma mass spectrometry. Because only metal ions can be iodinated with iohexol, interferences from the abundant organic molecules of plants that are confronted by secondary ion mass spectrometry (SIMS) are also greatly decreased.

Imaging the Dynamics of Metal Ion-Coupled Electron Transfer on Material Surfaces with Redox/Photo Active Chelators

“…25 Because of the complete atomization of metal ions in high-temperature plasma torch up to 8000 K, oxidation states and anions are not available with ICP MS. Through the formation of complexes or metal-iodide clusters, 26 identification of metal ions has been achieved with matrix-assisted laser desorption ionization MS (MALDI−MS) that can reveal not only identities but also oxidization states. In order to further monitor the dynamics of metal ion-coupled electron transfer, redox/photo active chelators were proposed in this work and applied to wide-field imaging of metal ions on material surfaces.…”