Stabilization of gas-phase uranyl complexes enables rapid speciation using electrospray ionization and ion mobility-mass spectrometry

Gas-phase synthesis of [OU-X]+ (X = Cl, Br and I) from a UO22+ precursor using ion-molecule reactions and an [OUCH]+ intermediate

Difficulty in the preparation of gas-phase ions that include U in middle oxidation states(III,IV) have hampered efforts to investigate intrinsic structure, bonding and reactivity of model species. Our group has used preparative tandem mass spectrometry (PTMS) to synthesize a gas-phase U-methylidyne species, [OUCH]+, by elimination of CO from [UO2(CCH)]+ [M. J. van Stipdonk, I. J. Tatosian, A. C. Iacovino, A. R. Bubas, L. Metzler, M. C. Sherman and A. Somogyi, J. Am. Soc. Mass Spectrom., 2019, 30, 796-805], which has been used as an intermediate to create products such as [OUN]+ and [OUS]+ by ion-molecule reactions. Here, we investigated the reactions of [OUCH]+ with a range of alkyl halides to determine whether the methylidyne is a also a useful intermediate for production and study of the oxy-halide ions [OUX]+, where X = Cl, Br and I, formally U(IV) species for which intrinsic reactivity data is relatively scarce. Our experiments demonstrate that [OUX]+ is the dominant product ion generated by reaction [OUCH]+ with neutral regents such as CH3Cl, CH3CH2Br and CH2CHCH2I.

Electrospray Ionization Ion Mobility Mass Spectrometry

Electrospray ionization ion mobility mass spectrometry (ESI-IMS-MS) is a rapidly progressing analytical technique for the examination of complex compounds in the gas phase. ESI-IMS-MS separates isomers, provides structural information, and quantitatively identifies peptides, lipids, carbohydrates, polymers, and metabolites in biological samples. ESI-IMS-MS has pharmaceutical, environmental, and manufacturing applications quickly characterizing drugs, petroleum products, and metal macromolecules. This review provides the history of ESI-IMS-MS development and applications to date.

Recent Approaches for Chemical Speciation and Analysis by Electrospray Ionization (ESI) Mass Spectrometry

In recent years, the chemical speciation of several species has been increasingly monitored and investigated, employing electrospray ionization mass spectrometry (ESI-MS). This soft ionization technique gently desolvates weak metal–ligand complexes, taking them in the high vacuum sectors of mass spectrometric instrumentation. It is, thus, possible to collect information on their structure, energetics, and fragmentation pathways. For this reason, this technique is frequently chosen in a synergistic approach to investigate competitive ligand exchange-adsorption otherwise analyzed by cathodic stripping voltammetry (CLE-ACSV). ESI-MS analyses require a careful experimental design as measurement may face instrumental artifacts such as ESI adduct formation, fragmentation, and sometimes reduction reactions. Furthermore, ESI source differences of ionization efficiencies among the detected species can be misleading. In this mini-review are collected and critically reported the most recent approaches adopted to mitigate or eliminate these limitations and to show the potential of this analytical technique.

Stepwise optimization of a Flexible Microtube Plasma (FµTP) as an ionization source for Ion Mobility Spectrometry

The ionization source is the central system of analytical devices such as mass spectrometers or ion mobility spectrometers. In this study, a recently developed flexible microtube plasma (FμTP) is applied as an ionization source for a custom-made drift tube ion mobility spectrometer (IMS) for the first time. The FµTP is based on a highly miniaturized, robust and a small-footprint dielectric barrier discharge design with an outstanding ionization efficiency. In this study, the experimental setup of the FµTP was further improved upon to achieve optimal coupling conditions in terms of the ion mobility spectrometry sensitivity and the plasma gas consumption. One major focus of this study was the adjustment of the electrical operation parameters, in particular, the high voltage amplitude, frequency and duty cycle, in order to minimize the electric field disturbances and yield higher signals. Additionally, the consumption of helium plasma gas was reduced by refining the FµTP. It was found that the ionization efficiency could be significantly enhanced by increasing the plasma high voltage and through application of a duty cycle up to 90:10. Plasma gas flows could be reduced down to 3 mL min^-1 by increasing the plasma high voltage amplitude. Furthermore, a smaller wire electrode design enables the operation of the FµTP with nitrogen and clean air. Moreover, detection limits of a homologous series of ketones in the range of 330 ppt_v (N₂-FµTP, 2-decanone) down to 20 ppt_v (He-FµTP, 2-octanone) could be reached in the optimized setup. To sum up, this feasibility study demonstrates the potential of the optimized FµTP as a powerful ionization source for ion mobility spectrometry especially with regard to ionization efficiency.