ORCID Identifier(s)

0000-0003-0834-8012

Graduation Semester and Year

2019

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Chemistry

Department

Chemistry and Biochemistry

First Advisor

Kevin A Schug

Abstract

Coupling supercritical fluid extraction (SFE) on-line with supercritical fluid chromatography (SFC) – tandem mass spectrometry (MS/MS) provides a platform for extraction, separation, and detection in a single analysis. Utilization of this technique simplifies sample preparation while limiting sample loss and/or contamination and significantly decreases total analysis time. SFE-SFC-MS/MS requires consideration of many extraction and chromatographic variables to not only provide the most efficient extraction, but to analytically transfer the extracted analytes to the column for separation. There is a fundamental lack of understanding of how the variables in SFE affect those in SFC. In the first study, on-line SFE-SFC-MS/MS was applied for the determination of polycyclic aromatic hydrocarbons (PAHs) in soil. The purpose of this study was to develop and validate the first on-line SFE-SFC-MS/MS method for the quantification of PAHs in various types of soil. Parameters for on-line extraction coupled to chromatographic analysis were optimized. The method was validated for concentrations of 10–1500 ng of PAHs per gram of soil in Certified Reference Material (CRM) sediment, clay, and sand with R2≥0.99. Limits of detection (LOD) were found in the range of 0.001–5 ng/g, and limits of quantification (LOQ) in the range of 5–15 ng/g. The method developed in this study can be effectively applied to the study of PAHs in the environment, and lays the foundation for further applications of on-line SFE-SFC-MS. Typically, a univariate approach is taken in on-line SFE-SFC-MS/MS method development which provides little insight into how the variables work together. In the second study, a multivariate approach was used to develop a better understanding of the synergistic relationship between the extraction and separation processes by focusing on the optimization of extraction parameters for target analytes with a wide range of physicochemical properties in matrices of variable retentivity. Optimal extraction parameters were determined for 18 analytes in three variable sample types. Compromise in optimal extraction parameters must be made when simultaneously extracting and analyzing a significantly wide range of analytes. Detection of drugs of abuse (DoA) in hair; being a convenient and noninvasive technique for the determination of controlled substances, is important in forensics and toxicology. SFE-SFC-MS/MS being ideal for DoA determination in complex matrices, provides a highly specific and sensitive chemical analysis while limiting the need for extensive manual sample preparation. Supercritical fluid extraction of seventeen DoAs from human hair was performed on-line using carbon dioxide (CO₂) with 5 mM ammonium formate in methanol. Optimal conditions for simultaneously extracting 17 drugs of abuse were predicted using models developed by response surface methodology. Multivariate analysis was used to optimize extraction parameters, including time (static and dynamic), modifier concentration, flow rate and extraction pressure. It was determined that a compromise between flow rate and concentration was required. Optimal extraction occurred using 15% modifier at 5.00 mL/min for an 8 minute static extraction followed by 15 minutes of dynamic flow at 2 % modifier with a 30 °C extraction vessel temperature and dual backpressures of 10.0 MPa. Significant performance differences were observed between the extraction of standard analytes spiked onto blank hair samples and extraction of a known drug user’s hair where the analytes of interest were incorporated into hair growth. The known drug user’s hair required multiple extractions to liberate the illicit substance from the complex hair matrix. The amount of analyte extracted during a third round of extractions was observed at double the amount extracted in the first extraction. In samples with spiked on analytes, the amount of extracted analyte decreased with each consecutive extraction. More work is needed to address the matrix effects of drugs incorporated into hair. Most methods developed for hair analysis rely upon spiked samples; however, it appears that a spiked sample versus an incorporated sample may not be comparable. Determining a better method for incorporating standards into hair will provide the basis for an improved extraction and quantification.

Keywords

Method development, Multivariate analysis, Sample preparation, Environmental analysis, Forensics analysis

Disciplines

Chemistry | Physical Sciences and Mathematics

Comments

Degree granted by The University of Texas at Arlington

Included in

Chemistry Commons

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