Date of Award
8-2025
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Chemistry
Committee Chair/Advisor
R. Kenneth Marcus
Committee Member
George Chumanov
Committee Member
Christopher Chouinard
Committee Member
Brian Powell
Abstract
The liquid sampling – atmospheric pressure glow discharge (LS-APGD) ionization source is a novel microplasma ionization source capable of ionizing a diverse set of both inorganic and organic chemical species including, ionic metal constituents as well as ligated metallic species, polyaromatic hydrocarbons (PAH), halogens, proteins, and even per/poly fluorinated alkyl substances (PFAS). The ability to generate ions from diverse chemical species, known as combined atomic and molecular (CAM) ionization, is not found with traditional ionization sources. In addition, the LS-APGD is capable of coupling with mass spectrometer platforms typically reserved for “organic” mass spectrometry, such as the high-resolution Orbitrap mass spectrometer platform, without the high gas flow, solution flow and power requirements of typical inorganic ion sources (i.e., inductively coupled plasma). The LS-APGD and the Orbitrap mass spectrometer coupling represent a high-resolution mass spectrometric platform that can leverage the high mass resolution to overcome isobaric interferences in inorganic analysis. Traditionally, isobaric interference requires prior separations to remove the isobaric interferent before the analysis of the analyte of interest. With the LS-APGD / Orbitrap coupling offering a baseline resolution of 70,000 (at m/z 200), many isobaric interferences can be separated in the mass spectrum without resorting to costly, time-consuming sample manipulations prior to measurement. In addition, by using external data acquisition systems such as the Spectroswiss FTMS Booster, the mass resolution can be increased to ~1,000,000, potentially eliminating most isobaric interferents. The use of high mass resolution has numerous benefits to the nuclear forensics and safeguarding communities, including significant time savings by reducing complex separations. In addition, by eliminating the need for separations, measurements can be taken directly from environmental swipes using microextractions without impact from other species that may be present on the swipe surface. Using microextractions to analyze the swipe surface directly will result in more representative uranium isotope ratio measurements since they are not biased by the uranium bound in the cotton swipe, which contributes to the traditional bulk digestion measurement. In addition, using microextractions allows for spatial resolution across the swipe surface, which allows for more understanding of the uranium enrichment levels and activities within the investigated facility.
The works presented in this document are the first steps towards demonstrating the capabilities of the LS-APGD / Orbitrap platform for routine analysis of environmental swipes. Studies were conducted using moving average data processing methodologies to improve uranium isotope ratio measurements for transient signals. In addition, an uncertainty budget was generated for uranium isotope ratio measurements, presenting each measurand's individual contribution to total measurement uncertainty. The LS-APGD / Orbitrap coupling capabilities were also expanded to other actinides by the measurement of plutonium. Finally, the use of high mass resolution was used to measure uranium isotope ratios in the presence of high concentrations of Pb, Pt, Ta, and W; these elements form polyatomic isobaric interference that hampers uranium isotope ratio measurements with ICP-MS, thus demonstrating the power of interference-free isotope ratio measurements using mass resolution alone. These experiments mark essential milestones towards using microextraction / LS-APGD /Orbitrap for isotope ratio determinations directly from environmental swipes for the nuclear forensics and safeguarding communities.
Recommended Citation
Goodwin, Joseph V., "Progress Towards Uranium Isotope Ratio Measurements Directly from Cotton Swipes with the Liquid Sampling – Atmospheric Pressure Glow Discharge (LS-APGD) Ionization Source" (2025). All Dissertations. 4067.
https://open.clemson.edu/all_dissertations/4067
Author ORCID Identifier
https://orcid.org/0000-0001-7086-5390
Comments
The nuclear forensics and safeguarding communities consider environmental swipes to be one of the most important tools that on-site investigators can use to determine the correctness of states' declarations about the ongoing enrichment activities at the investigated facility. All nuclear activities release a small amount of material to the environment that collects on surfaces; this released material can then be collected by the investigator using environmental swipes. These are typically analyzed by digesting the entire swipe. This process could bias the isotope ratio (how enriched the sample is or how much 235U is present relative to 238U) results found due to the background natural uranium present bound within the swipe itself. By using microextraction techniques, the swipe surface is directly integrated, and the particulates found on the swipe surface are analyzed without needing to digest the entire swipe, removing the possibility of biasing the result with the bound natural uranium. In addition, the microextraction approach to swipe analysis is significantly faster and simpler than the digestion method.
To use microextractions directly from the swipe surface, potential interferences from other species that may be present need to be eliminated. With the traditional digestion approach, several time-consuming and labor-intensive chemical work-ups are performed to remove the possibility of interferences. When directly analyzing from the swipe surface, mass spectrometers with a higher resolution than those typically used could separate the interferences from the uranium signal to get accurate uranium isotope ratio measurements. However, these high mass resolution instruments are incompatible with traditional ionization sources. The liquid-sampling atmospheric pressure (LS-APGD) ionization source is a small microplasma ionization source capable of ionizing uranium and using high-resolution mass spectrometers such as the Orbitrap. Combining the microextraction technique with the LS-APGD / Orbitrap platform provides an ideal solution to routine analysis of environmental swipes; microextraction removes the bias from the bound uranium within the swipe while greatly reducing the analysis time, and high mass resolution removes the interferences. Significant milestones towards routine microextraction / LS-APGD / Orbitrap analysis of environmental swipes are reported herein. These milestones include developing new data processing techniques, understanding measurement uncertainty, analyzing plutonium, and overcoming isobaric interferences using high mass resolution.