9 research outputs found
Initial Characterization and Optimization of the Liquid Sampling-Atmospheric Pressure Glow Discharge Ionization Source Coupled to an Orbitrap Mass Spectrometer for the Determination of Plutonium
Plutonium
measurements are essential to the nuclear forensics and
safeguards community. The liquid sampling-atmospheric pressure glow
discharge (LS-APGD) microplasma ionization source coupled with an
Orbitrap mass spectrometer is a proven platform for uranium isotope
ratio determinations. This work expands the LS-APGD-Orbitrap platform
capabilities by reporting the first-ever analysis of plutonium with
the LS-APGD and the first-ever measurement of elemental plutonium
with an Orbitrap mass spectrometer. This coupling has the potential
to dramatically reduce the complex sample manipulations required for
traditional analysis techniques employed for actinide isotope ratio
determinations. As a first step toward the goal of simultaneous uranium
and plutonium isotope ratio determinations, the initial characterization
and optimization of the platform for the detection of plutonium are
reported. Collision-induced dissociation modality settings were optimized
to reduce water-related and other molecular clusters containing plutonium,
maximizing 242Pu16O2+ responses.
A design of experiments study was conducted to optimize the discharge
conditions of the dual-electrode LS-APGD toward the responsivity of 242Pu16O2+. The measurement
sensitivity was determined from a Pu response curve, yielding a limit
of detection of 10 fg (absolute) of total analyte when data was collected
and processed with a Spectroswiss FTMS Booster X2 data acquisition
system. Additionally, plutonium and uranium were measured in a simultaneous
acquisition, and each analyte remained unaffected by the other. It
is believed that the LS-APGD-Orbitrap platform could be a valuable
addition to the nuclear forensics’ toolbox and, indeed, other
scientific disciplines and regulatory communities in which rapid,
high-resolution plutonium determinations are paramount
Ionization thresholds of small carbon clusters: tunable VUV experiments and theory
Abstract Small carbon clusters (C n , n=2-15) are produced in a molecular beam by pulsed laser vaporization and studied with vacuum ultraviolet (VUV) photoionization mass spectrometry. The required VUV radiation in the 8-12 eV range is provided by the Advanced Light Source (ALS) at the Lawrence Berkeley National Laboratory. Mass spectra at various ionization energies reveal the qualitative relative abundances of the neutral carbon clusters produced. By far the most abundant species is C 3 . Using the tunability of the ALS, ionization threshold spectra are recorded for the clusters up to 15 atoms in size. The ionization thresholds are compared to those measured previously with charge transfer bracketing methods. To interpret the ionization thresholds for different cluster sizes, new ab initio calculations are carried out on the clusters for n=4-10. Geometric structures are optimized at the CCSD(T) level with cc-pVTZ (or cc-pVDZ) basis sets, and focal point extrapolations are applied to both neutral and cation species to 2 determine adiabatic and vertical ionization potentials. The comparison of computed and measured ionization potentials makes it possible to investigate the isomeric structures of the neutral clusters produced in this experiment. The measurements are inconclusive for the n=4-6 species because of unquenched excited electronic states. However, the data provide evidence for the prominence of linear structures for the n = 7, 9, 11, 13 species and the presence of cyclic C 10
Rare Earth Element Determination in Uranium Ore Concentrates Using Online and Offline Chromatography Coupled to ICP-MS
The determination of trace elements, particularly rare earth elements, in uranium ore concentrates (UOCs) is important as the pattern can be indictive ore characteristics. Presented here is a methodology for accurately quantifying rare earth elements (REE) in UOCs. To improve the measurement uncertainty, isotope dilution mass spectrometry (IDMS) was utilized over other quantification techniques such as external calibration or standard addition. The isotopic determinations were measured by inductively coupled plasma-mass spectrometry (ICP-MS). To obtain high-fidelity isotopic measurements, separation of the REE from the uranium matrix was achieved by high-performance ion chromatography (HPIC), reducing the isobaric interferences. After separation, the target analytes were analyzed in two different modalities. For high precision analysis, the separated analytes were collected and measured by ICP-MS in an “offline” fashion. For a rapid approach, the separated analytes were sent directly into an ICP-MS for “online” analysis. These methods have been demonstrated to accurately quantify the REE content in a well-characterized UOC sample
Automated Separation of Uranium and Plutonium from Environmental Swipe Samples for Multiple Collector Inductively Coupled Plasma Mass Spectrometry
A fully
automated method for the separation of low-concentration uranium from
plutonium in environmental swipe samples has been developed. The offline
chromatography system features renewable 1 mL Eichrom TEVA and UTEVA
column generation from bulk resin slurry. Discrete fractions of the
separated actinides are delivered into user defined vials for future
analysis. Clean room background levels were achieved outside of a
cleanroom environment with this method. Purification of uranium and
plutonium from various sample matrixes and at various concentrations
was successful. Major and minor isotope ratios for both elements were
measured via multiple collector inductively coupled plasma mass spectrometry
and were in good agreement with certified reference values. Validation
of the separation method was conducted on archived environmental samples
and agreed with values previously reported using standard column chemistry
Analysis of Clostridium botulinum Serotype E Strains by Using Multilocus Sequence Typing, Amplified Fragment Length Polymorphism, Variable-Number Tandem-Repeat Analysis, and Botulinum Neurotoxin Gene Sequencingâ–ż
A total of 41 Clostridium botulinum serotype E strains from different geographic regions, including Canada, Denmark, Finland, France, Greenland, Japan, and the United States, were compared by multilocus sequence typing (MLST), amplified fragment length polymorphism (AFLP) analysis, variable-number tandem-repeat (VNTR) analysis, and botulinum neurotoxin (bont) E gene sequencing. The strains, representing environmental, food-borne, and infant botulism samples collected from 1932 to 2007, were analyzed to compare serotype E strains from different geographic regions and types of botulism and to determine whether each of the strains contained the transposon-associated recombinase rarA, involved with bont/E insertion. MLST examination using 15 genes clustered the strains into several clades, with most members within a cluster sharing the same BoNT/E subtype (BoNT/E1, E2, E3, or E6). Sequencing of the bont/E gene identified two new variants (E7, E8) that showed regions of recombination with other E subtypes. The AFLP dendrogram clustered the 41 strains similarly to the MLST dendrogram. Strains that could not be differentiated by AFLP, MLST, or bont gene sequencing were further examined using three VNTR regions. Both intact and split rarA genes were amplified by PCR in each of the strains, and their identities were confirmed in 11 strains by amplicon sequencing. The findings suggest that (i) the C. botulinum serotype E strains result from the targeted insertion of the bont/E gene into genetically conserved bacteria and (ii) recombination events (not random mutations) within bont/E result in toxin variants or subtypes within strains