Graduation Semester and Year

2021

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Chemistry

Department

Chemistry and Biochemistry

First Advisor

Kevin A Schug

Abstract

In analytical chemistry the term “headspace” refers to the vapor that forms above a sample (liquid or solid) in a closed container. Headspace (HS) sampling is the method to promote partition between volatile components from the sample matrix and then analyzed by gas chromatography (GC). HS is an excellent technique to introduce a “clean” vapor sample into the GC and avoids introduction of non-volatile components from the sample matrix and often used for determination of volatile organic compounds (VOCs) with minimal or no additional sample preparation. Concerns about the environmental impact of fossil fuel extraction techniques (i.e., hydraulic fracturing and other well stimulation techniques) have risen due to its expansion in the United States and other countries. Robust atmospheric studies have attributed to the emissions of rogue greenhouse gases and VOCs to mechanical inefficiencies commonly found in the midstream production process, such as gas flaring stations, condensate tanks, and pipelines. However, the interplay between fossil fuel extraction activities and soil quality has not received much attention. Utilizing headspace gas chromatography mass spectrometry (HS-GC-MS) and an establish standard method by the Environmental Protection Agency (EPA), we present a study of soil near oil and gas production in verified emissions of volatile contaminants. The findings provide an initial indication of the interactions between atmospheric VOCs contamination events and the accumulation of those contaminants in soil where, varying soil texture was found to contribute to total amount detected. Room temperature ionic liquids (RTILs) have received significant attention in HS analysis due to their unique physiochemical properties (i.e., negligible vapor pressures, tunable thermal stabilities, tunable viscosities and wide liquid range). RTILs are salts in which ions are poorly coordinated, resulting in a liquid state at room temperature. The evaluation of RTILs as co-solvent in soil analysis, in an effort to increase sensitivity, reduce and normalized the matrix-effects associated with varying soil compositions. It was found that hydrophilic RTILs investigated, 1-ethyl-3-methylimidazolium ethylsulfate ([EMIM][ESO4]), 1-ethyl-3-methylimidazolium diethyl phosphate ([EMIM][DEP]), tris(2-hydroxyethyl)methylammonium methylsulfate ([MTEOA][MeOSO3]), reduced matrix-effect from varying soil composition thus, reducing the need to characterized and matrix-match soil textures for calibration purposes. It also reduced the analysis time and increased precision and accuracy for the quantification of VOCs in variable soil matrices relative to standard methods. Understanding the thermodynamic interactions between an analyte and the sample phase is of paramount importance when eliciting a co-solvent in HS analysis. The partition coefficient (KP) is an equilibrium constant that describes the distribution of the analyte between two phases (i.e., sample phase/ gas phase). Kp determinations by HS-GC is acquired by two methods: vapor phase calibration (VPC) and phase ratio variation (PRV). Kp determinations of analytes in HS co-solvents can help guide the analyst in which to use for the analysis at hand. Here we demonstrate the ability of using a pressurized – loop HS system in conjunction with gas chromatography vacuum ultraviolet detection (HS-GC-VUV) to directly calculate the concentration of the analyte in the gas phase, by pseudo-absolute quantification (PAQ), thus allowing for quick determination of Kp and other thermodynamic properties such as enthalpy ( ∆H )and entropy (∆S ) of the system. The Kp determinations by PAQ were comparable to those obtained using the VPC method, with differences in the average values ranging <1 to 30%.

Keywords

Headspace analysis, Soil analysis, Gas chromatography, Mass spectrometry, Vacuum ultraviolet detection, Pseudo absolute quantification, Environmental contaminants, Partition coefficient, Enthalpy, Entropy, Thermodynamics, Van't Hoff plots

Disciplines

Chemistry | Physical Sciences and Mathematics

Comments

Degree granted by The University of Texas at Arlington

Included in

Chemistry Commons

Share

COinS