Matrix-Assisted Ionization of Molecular Uranium Species

Abstract

Matrix-assisted ionization (MAI) demonstrates high sensitivity for a variety of organic compounds; however, few studies have reported the application of MAI for the detection and characterization of inorganic analytes. Trace-level uranium analysis is important in the realms of nuclear forensics, nuclear safeguards, and environmental monitoring. Traditional mass spectrometry methods employed in these fields require combinations of extensive laboratory chemistry sample preparation and destructive ionization methods. There has been recent interest in exploring ambient mass spectrometry methods that enable timely sample analysis and higher sensitivity than what is attainable by field-portable radiation detectors. Rapid characterization of uranium at nanogram levels is demonstrated in this study using MAI techniques. Mass spectra were collected on an atmospheric pressure mass spectrometer for solutions of uranyl nitrate, uranyl chloride, uranyl acetate, and uranyl oxalate utilizing 3-nibrobenzonitrile as the ionization matrix. The uranyl complexes investigated were detectable, and the chemical speciation was preserved. Sample analysis was accomplished in a matter of seconds, and limits of detection of 5 ng of uranyl nitrate, 10 ng of uranyl oxalate, 100 ng of uranyl chloride, and 200 ng of uranyl acetate were achieved. The observed gas-phase speciation was similar to negative-ion electrospray ionization of uranyl compounds with notable differences. Six matrix-derived ions were detected in all negative-ion mass spectra, and some of these ions formed adducts with the uranyl analyte. Subsequent analysis of the matrix suggests that these molecules are not matrix contaminants and are instead created during the ionization process.

Direct sub‐atmospheric pressure ionization mass spectrometry: Evaporation/sublimation‐driven ionization is amazing, fundamentally, and practically

“…Only low abundant matrixderived ions are detected, contrary to other work. 70 Key advantages of MAI are ease and speed of analysis, high sensitivity and minute sample volume requirements, potential for spatially-resolved surface analyses, robustness of the experiment, and ease of use. 5,13,14 These and other studies were significantly aided by dedicated source developments, as described in this paper.…”

A tutorial: Laserspray ionization and related laser‐based ionization methods for use in mass spectrometry

“…The novel ionization processes using inlets for ESI sources of ultrahigh resolution mass spectrometers show the typical resolution and mass accuracy related to each instrument (Chen et al, 2014(Chen et al, , 2016(Chen et al, , 2018Cody, 2018;Harron et al, 2013;Mannion et al, 2021;Trimpin, Thawoos, et al, 2016b;, but, contrary to ESI, these measurements are rapid and, contrary to MALDI, proteins can be detected on these instruments because of the multiple charging. An outstanding application of the use of 2-NPG includes that of antibodies using a TOF mass spectrometer for ionizing in the linear detection mode proteins at least as large as ~150 kDa (Choi et al, 2019).…”

“…In another example, lanthanide‐containing complexes were detected, and in some cases imaged, using the 2‐NPG matrix (Trimpin, Yenchick, et al, 2023; Vithanarachchi et al, 2016). Uranium salts have been analyzed using MAI (3‐NBN matrix) based on inlet ionization (Mannion et al, 2021).…”

LDRD External Report Summary

“…Matrix-Assisted Ionization (MAI) is one of the most recently discovered ambient mass spectrometry techniques, wherein ions are produces without the application of heat, photons, electrons, or high voltage as required for conventional mass spectrometry (Figure 1). 1,2 Although SRNL was the first to demonstrate that this technique could be used to ionize inorganic compounds in aqueous solutions, 3 the underlying ionization phenomena remains uncharacterized. 1,[4][5][6][7][8][9][10] This effort seeks to examine fundamental aspects of MAI via a combination of mass spectrometry experiments, x-ray diffraction of MAI matrix chemicals, and modeling/simulation.…”