Graduation Year

2010

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Chemistry

Major Professor

Abdul Malik, Ph.D.

Keywords

Sol-gel, Silica, Titania, Germania, CME, SPME, In-tube SPME, High-performance liquid chromatography, Solvent resistance, pH stability

Abstract

High-performance liquid chromatography (HPLC) is the most widely used analysis technique. However, its sensitivity is limited. Sample preconcentration methods, such as fiber-based solid-phase microextraction (SPME) and in-tube SPME (capillary microextraction) offer improved detection limits. It is, however, difficult to couple fiber SPME on-line with HPLC due to the need for complicated desorption devices. Such coupling is further complicated due to the limited solvent stability of the extracting phase both in the fiber and in-tube formats of SPME. In this research, surface-bonded sol-gel sorbents were developed to provide the solvent stability required for effective on-line hyphenation of capillary microextraction (CME) with HPLC. These sol-gel sorbents were prepared using (1) silica-based, (2) titania-based, and (3) germania-based sol-gel precursors.

Sol-gel reactions were performed within fused silica capillaries to create a number of organic-inorganic hybrid sorbents in the form of surface-bonded coatings: (1) alkyl (methyl, octyl, octadecyl), (2) polydimethyldiphenylsiloxane, (3) titania poly(tetrahydrofuran), and (4) germania tri-block polymer. The sol-gel coated microextraction capillaries were capable of efficiently extracting a wide variety of analytes, including polycyclic aromatic hydrocarbons, ketones, aldehydes, aromatic compounds, amines, alcohols, and phenols with ng/L to pg/L detection limits. The sol-gel methyl coating demonstrated a counterintuitive ability to extract polar analytes. Sol-gel polydimethyldiphenylsiloxane coatings were found to be resistant to high temperature solvent exposure (150°C and 200°C), making them suitable for use in high-temperature liquid phase separations.

To better understand how extraction takes place, effects of alkyl chain length and sol-gel precursor concentration were evaluated in the study on sol-gel alkyl coatings. The sol-gel titania poly(tetrahydrofuran) coating was also capable of extracting underivatized aromatic acids and polypeptides at pHs near their respective isolectric points. The sol-gel titania poly(tetrahydrofuran) coatings and the sol-gel germania tri-block polymer coatings demonstrated impressive resistance to extreme pH conditions, surviving prolonged exposure to 1.0 M HCl (pH approx. 0.0) and 1.0 M NaOH (pH approx. 14.0) with virtually no change in extraction behavior. Sol-gel germania tri-block polymer coatings were also stable under high temperature solvent conditions (200°C). In addition, for the first time, the analyte distribution constants between a sol-gel germania coating and the aqueous samples (Kcs) were determined.

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