Graduation Year

2017

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Chemistry

Major Professor

Abdul Malik, Ph.D.

Committee Member

Li-June Ming, Ph.D.

Committee Member

Aydin Sunol, Ph.D.

Committee Member

Theresa Evans-Nguyen, Ph.D.

Keywords

Sol-gel sorbents, Capillary microextraction, Solid Phase Microextraction, Perfluorinated ligands, Hydrophobic Interaction, Germania-based sorbents

Abstract

Sample preparation is the most time-consuming and error-prone step in chemical analysis. Miniaturization and automation of the sample preparation equipment eliminating or reducing the use of hazardous organic solvents, online hyphenation of sample preparation with analytical instruments in a cost-effective way are important factors that need to be considered to design and implement innovative sample preparation techniques and strategies. Solid-phase microextraction (SPME) is a simple, environmentally benign technique well suited for hyphenation with analytical instruments. However, poor coating stability is a significant drawback of SPME employing conventionally prepared coatings. This shortcoming arises from the lack of chemical bonding between the sorbent coating and the substrate. Introduction of sol-gel coatings in SPME greatly improved thermal stability and solvent stability in SPME, by providing direct chemical bonding between substrate and the sol-gel coating. In traditional fiber format of SPME (where the sorbent coating is placed on the outer surface of an end-segment of the fiber) the coating remains vulnerable to mechanical damage. Capillary microextraction (CME), the capillary format of SPME (also known as in-tube SPME), allows to overcome this shortcoming by securing the sorbent coating on inner walls of the capillary. This dissertation focuses on the development and systematic investigation of novel silica- and germania-based perfluorinated and non-fluorinated sol-gel sorbents in the form of CME surface coatings: their preparation, material characterization, CME performance evaluation, preconcentration and recovery of various analytes including environmental pollutants. This research established that germania-based sol-gel sorbents are characterized by superior microextraction performance than analogous silica-based sorbents. This enhanced performance provided by germania-based sol-gel sorbents may be explained based on thermogravimetric analysis suggests that higher carbon loading on germania-based sol-gel sorbents. Germania-based phenyl- (Ph), phenethyl- (PhE), octyl- (C8), octadecyl- (C18) and cyclohexenylethyl- (ChE) ligand-containing sol-gel sorbents were prepared and various pollutants with aromatic rings (such as aromatic ketones, aldehydes and polycyclicaromatic hydrocarbons) were extracted and analyzed by CME-GC and CME-HPLC. It was observed that sol-gel sorbents containing aromatic ligands (PhE and Ph) provided superior microextraction performance for the analytes with aromatic ring(s) in their structure, than the sorbents with aliphatic ligands (C8 and C18). Investigation of sol-gel sorbents containing hydrophobic perfluorooctyl (PF-C8) and perfluorododecyl (PF-C12) ligands revealed that PF-C8 and PF-C12 sol-gel sorbents provided ~ 3 times higher microextraction efficiency (measure in terms of specific extraction, SE) than corresponding non-fluorinated counterparts, C8- and C12-, respectively. The synthesis and design of silica- and germania-based dual ligands sol-gel sorbents simultaneously providing superhydrophobicity and π-π interactions with analytes represent a significant accomplishment of this research. Such sorbents contained a PF-C12 and PhE ligands incorporated in sorbent chemical structure. In this case, perfluoro- group provided enhanced hydrophobic interaction and PhE group provided π-π interaction with the analytes. Combination of such interactions proved to be quite effective in the microextraction of alkylbenzenes and related compounds. Dual-ligand sol-gel sorbents with both equimolar and non-equimolar ligand concentrations were prepared. Experimentally it was established that sorbents with higher perfluorinated alkyl ligand concentrations had higher affinity for aliphatic hydrocarbons; however; when PhE concentration was higher, the dual-ligand sorbent showed enhanced affinity for aromatic compounds. The prepared sol-gel sorbents were characterized by less than 5% run-to-run RSD values, and also less than 5% capillary-to-capillary RSD values, which indicate that the sol-gel technique used in sorbent preparation was highly reproducible. The prepared sol-gel sorbents also showed that their performance does not deteriorate under aqueous saline matrix; therefore, it could be useful in the microextraction of pollutants from ocean water.

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