Date of Award
Master of Science (MS)
R. Kenneth Marcus
Carlos D. Garcia
The liquid sampling – atmospheric pressure glow discharge (LS-APGD) coupled to an ultra-high resolution Orbitrap mass spectrometer has demonstrated expanded abilities for the uranium isotope ratios and molecular analysis by adding low polarity polyaromatic hydrocarbons (PAHs) to its already impressive repertoire. The LS-APGD/Orbitrap combination has shown the ability to analyze all three natural isotopes of uranium, 234U, 235U, and 238U, simultaneously. This is different from traditional instruments use a scanning type mass analyzer, but the Orbitrap analyzes all analytes simultaneously. Traditionally, in order to analyze both uranium and PAHs, two entirely different instruments would be required, typically an inductively coupled plasma mass spectrometer (ICP-MS) for uranium analysis and an atmospheric pressure chemical ionization source coupled to a mass spectrometer. However, with the LS-APGD, a simple switch in the carrier solution allows for these analyses. The International Atomic Energy Agency (IAEA) sets international target values (ITVs) for measurement uncertainty for uranium analysis. The LS-APGD/Orbitrap has shown the ability to meet these international target values, upon the addition of an external data acquisition system (DAQ), this pairing expanded on this analysis by adding in the ability to measure 234UO2, while still maintaining the high precision measurement of 235UO2. On top of this, the external DAQ allowed for a resolution improvement of 10x that of the standard system to be afforded and a limit of detection (LOD) of <13 pg mL-1¬ has been realized. By simply switching to MeOH:H2O from the standard 2% HNO3, the analysis of PAHs was realized, and more interesting, the observation of a protonated molecular ion was seen. This protonated molecular ion was not expected as there is not traditional site for protonation on these molecules that would afford facile protonation as do small molecular species. It was found that plasma conditions that result in higher rotational temperatures provide more protonation of these molecules, suggesting that more energy is necessary for the protonation. Along with the protonation being investigated, LODs from 110 pg mL-1 to 28 ng mL-1 were found. These LODs are comparable to those that are listed in EPA method 610.
Bills, Jacob R., "Liquid Sampling–Atmospheric Pressure Glow Discharge Ionization Source Coupled to an Ultra High Resolution Orbitrap Mass Spectrometer for Diverse Spectrochemical Analysis" (2021). All Theses. 3584.