Doctor of Philosophy (PhD)
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Quality control, non-target analysis, liquid chromatography, mass spectrometry, environmental chemistry, analytical chemistry, chemical space, electrospray ionization, atmospheric pressure chemical ionization, polydimethylsiloxane (PDMS), organic contaminants, remediation
Date of Defense
The first part of this dissertation will focus on the development of a simple, robust online solid phase extraction liquid chromatography high resolution mass spectrometry (SPE LC-HRMS) method followed by the use of computational software workflows for non-target analysis (NTA) of environmental samples (development). The benchmarks to assess reproducibility are not well defined for non-target analysis. Parameters to evaluate analytical performance, such as accuracy, precision and selectivity, are well defined for target analysis, but remain elusive for non-target screening analysis. In this study, quality control (QC) guidelines are proposed to assure reliable data in NTA methodologies using a simple set of standards. We have specifically evaluated method specificity, precision, accuracy and reproducibility in terms of peak area and retention time variability, true positive identification rate, intraday and interday variations and the use of QC samples to reduce false positives.
The second part of this dissertation will focus on the evaluation of different bodies of water in order to characterize different sources (application). Here we have compared electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) for the detection and identification of organic contaminants in tap and surface waters from South Florida using a combination of Kendrick mass defect (KMD) plots and Van Krevelen diagrams (VKD). This work will lead to the creation of a unique “fingerprint” for each water body that can be used to track water quality and its point of impact. The chemical space coverage of both ESI and APCI for the purpose of non-targeted analysis was explored and documented with respect to the Environmental Protection Agency’s (EPA) ToxCast chemical library. In addition, the performance of the developed NTA workflow was evaluated by analyzing 10 complex mixtures from an inter-laboratory study as part of the EPA’s Non-Targeted Analysis Collaborative Trial (ENTACT).
The final part of this dissertation will focus on the development of a simple and inexpensive polydimethylsiloxane (PDMS) sponge composite for the adsorption and removal of pollutants from high flow systems. The work also explores if the polymer can be functionalized with activated charcoal to enhance its adsorption capabilities and copper to deactivate bacteria (remediation). The PDMS sponge composites worked as expected, showing adsorption potential dominated by equilibrium partitioning according to the compounds Log Kow. Adding activated charcoal to the polymer improved its adsorption capabilities. Copper is a biocide and functionalizing the polymer with it deactivated E. coli.
Previously Published In
Brian Ng, Natalia Quinete, Piero Gardinali. Assessing accuracy, precision and selectivity using quality controls for non-targeted analysis. Sci. Total Environ. 2020, 713, 136568.
Ng, Brian, "Non-Target Analysis Using High-Resolution Mass Spectrometry to Characterize and Remediate Urban Waters" (2021). FIU Electronic Theses and Dissertations. 4856.
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