A multitude of highly informative methods exist for the detection and quantification of nuclear materials in radioactive debris. However, the majority of these methods are focused on atomic feature characterization and provide little information regarding metal speciation. Atmospheric pressure ion mobility (AP-IMS) offers a tractable, field-compatible method to separate different chemical forms of the same metal in the gas phase based on differences in ion-neutral collision cross-section (Ω). Given that the gas-phase separation scheme uses ions originating from complex solutions, a detailed characterization of the solvation and ionization efficiencies for different metal complexes is necessary. Coupling a mass spectrometer to a custom AP-IMS provides the necessary information required to accurately identify the metal complexes and aid in the classification of naturally occurring metal complexes from anthropogenic sources. The detection of the gas-phase parent ions for non-covalently bound metal salts remains highly challenging using stand-alone mass spectrometers equipped with atmospheric pressure ionization sources. Solvation effects, complex instability, and in-source fragmentation significantly diminish the effectiveness of such systems to detect intact inorganic metal complexes. Control over the desolvation conditions and low-energy ion transfer entering the vacuum stage of a mass spectrometer provide characteristics of the complex which may not be acquired using either IM or MS alone. We show that AP-IMS coupled with MS can accurately detect the presence of these non-covalently bound metal ions with reproducible mass and mobility values. The reactivity and instability of the gas-phase metal complexes results in a variety of conformations as the ion traverses the drift-tube. Metal ligand species dissolved in DMSO as opposed to water, have been shown to entropically and enthalpically stabilize the metal ligand species in solution; the stabilizing effect is also observed when the metal-ligand species is softly transferred into the gas-phase using ESI. We report, for the first time, the ion-neutral collision cross-section and speciation of the metals salts: Uranium, Barium, Cesium, and Lanthanum with acetate, chloride and nitrate dissolved in 0.1% DMSO. The end-goal of this study is to develop a field-use instrument for rapidly isolating and collecting the previously mentioned metal complexes on a solid surface for future isotopic analysis.

Accurate mass and mobility speciation of metal complexes: Uranium, barium, cesium, and lanthanum

251st National Meeting (2016)

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