Analytical Chemistry Commons^™

The Fabrication And Integration Of Pillar Array Channels For Chip Based Separations And Analysis, Lisa Christine Taylor

Doctoral Dissertations

The fundamental motivations for scaling existing technological platforms down to lab on chip dimensions are applicable in nearly all scientific disciplines. These motivations include decreasing waste, improving throughput, and decreasing time consumption. Analytical tools, such as chromatographic separation devices, can additionally benefit from system miniaturization by utilizing wafer-level fabrication technology, allowing for the rational design and precise control of variables which ultimately affect separation performance. With the use of microfabrication techniques, we have developed an original processing sequence for the fabrication of silicon oxide enclosed pillar arrays integrated within a fluidic channel. These pillar arrays create a highly uniform submicron …

The Itinerant Position Of Yttrium As Evidenced By Carboxylic Acid Extractions, Dustin C Collier

Doctoral Dissertations

The rare-earth elements Y and La-Lu share many similar physical and chemical properties. These similarities are reflected by the difficulty in the complete separation of the rare earths, often requiring hundreds to thousands of stages for the production of pure rare earths. Yttrium, traditionally known to be separated with Ho, has also been observed to be separated with other elements within the lanthanide series, and even outside the bounds of the lanthanide series itself. Previous publications by several authors have indicated that steric factors could influence the position of Y in solvent extractions of the rare earths using carboxylic acid …

Development And Application Of Liquid Chromatography-Tandem Mass Spectrometry Methods To The Understanding Of Metabolism And Cell-Cell Signaling In Several Biological Systems, Jessica Renee Gooding

Doctoral Dissertations

Liquid chromatography tandem mass spectrometry has become a powerful tool for investigating biological systems. Herein we describe the development of both isotope dilution mass spectrometry methods and targeted metabolomics methods for the study of metabolic and cell-cell signaling applications.

A putative yeast enzyme was characterized by discovery metabolite profiling, kinetic flux profiling, transcriptomics and structural biology. These experiments demonstrated that the enzyme shb17 was a sedoheptulose bisphosphatase that provides a thermodynamically dedicated step towards riboneogenesis, leading to the redefinition of the canonical pentose phosphate pathway.

An extension of metabolic profiling and kinetic flux profiling methods was developed for a set …

Advanced Techniques In Mass Spectrometry For Qualitative And Quantitative Protein Characterization, Andrew Boissy Dykstra

Doctoral Dissertations

Though mass spectrometry has earned a central role in the field of proteomics due to its versatility in a wide range of experiments, challenges and complications are still encountered when using mass spectrometry to characterize protein structures, post-translational modifications (PTMs), and abundances. In this dissertation, analytical methods utilizing mass spectrometry have been developed to address challenges associated with both qualitative and quantitative protein characterization. The effectiveness of using multiple pepsin-like proteases, both separately and in mixtures, combined with online proteolysis using a special triaxial probe has been demonstrated on an amyloid beta peptide related to the onset of Alzheimer’s disease. …

Liquid Extraction Based Surface Sampling: Liquid Microjunction Surface Sampling Probes Coupled With Mass Spectrometry, Matthew John Walworth

Doctoral Dissertations

The direct sampling of analytes from surfaces under atmospheric conditions followed by mass spectrometric analysis is an ever expanding area of scientific research. Atmospheric pressure surface sampling and ionization techniques for mass spectrometry (MS) offer the ability to interrogate samples that could not be studied under vacuum conditions required of more traditional MS surface analysis techniques. The geometry and nature of materials or surfaces that can be analyzed has been greatly expanded as a result. This dissertation characterizes and shows applications of liquid microjunction surface sampling probe (LMJ-SSP) electrospray ionization systems. The presented work compares traditional analytical work flows with …

Non-Thermal Plasma Inactivation Of Bacillus Amyloliquefaciens Spores, Yaohua Huang

Masters Theses

Bacterial spores have remarkable resistance to a variety of harsh conditions, causing spoilage in food industry and becoming the primary bacterial agent in biowarfare and bioterrorism. In this study, inactivation mechanisms of Bacillus amyloliquefaciens (BA) spores by non-thermal plasma (NTP) were investigated by using Fourier-transform infrared spectroscopy (FTIR) as a major tool to exam spores after NTP treatment. Chemometric techniques, such as multivariate classification models based on soft independent modeling of Class Analogy (SIMCA) and Principal Component Analysis (PCA), were employed to identify functional group changes in FTIR spectra. The IR absorbance bands correlated to dipicolinic acid (DPA) decreased after …

The Elucidation Of Stationary Phase Treatment Effects In Enantiomeric Separations, Joel Garrett Putnam

Doctoral Dissertations

Acid/base modifiers are sometimes used as additives in the elution on columns packed with amylose tris(3,5-dimethylphenylcarbamate) stationary phase to separate enantiomers. When modifiers are removed from the mobile phase, the stationary phase is affected in ways that are not understood because of the lack of systematic studies, making the scale-up of preparative separations difficult to predict. Once a column has been exposed to these modifiers, the selectivity of certain pairs of enantiomers may change, for the better or the worse. Numerous pairs of molecules affected by this phenomenon are listed in the literature. Five pairs of these molecules were chosen, …

Thermally Robust Ald And Silver Nanocube Based Plasmonic Probe For High Temperature And Microfluidic Sers Measurement, Joshy Francis John

Doctoral Dissertations

Raman spectroscopy is normally a non-destructive, highly selective technique that has become an ubiquitous tool for analytical chemists. One of the primary limitations of Raman spectroscopy, however, is the relatively low cross-section of the technique. With signal enhancements relative to normal Raman scattering as high as 1011, the ultra-trace detection of adsorbates down to the single molecule level has been achieved with SERS. Despite the dramatic improvement in the sensitivity and the high selectivity afforded by the SERS method, the acceptance of SERS as a general analytical tool has been hindered by a lack of stability and reproducibility in the …

Surface-Enhanced Raman Scattering: Substrate Development And Applications In Analytical Detection, Deepak Bhandari

Doctoral Dissertations

To advance the capabilities of surface-enhanced Raman scattering (SERS), we developed a silver modified polypropylene filter (AgPPF) substrate which acts as a pseudo stationary phase in harvesting SERS signatures of so called "phytochemical estrogens" and other environmentally significant chemicals. To augment electron beam lithography (EBL) in SERS research, we also introduced an interesting nanotransfer printing (nTP) technique which could circumvent the low throughput and extremely high resolution (< 10 nm) limitations of EBL in designing advanced SERS substrates. In our study, a nominal average thickness of 10 nm silver on the polypropylene microfiber produced nanoglobules of less than 100 nm in diameter. This noble metal nanoroughened layer allowed AgPPF to serve as a SERS active substrate, onto which the noted endocrine disrupting chemicals were passed through and harvested. The intense, multifeatured vibrational Raman spectra of very rarely SERS studied chemical species collected indicates the potential for useful detection via this approach of creating SERS substrates. AgPPF substrates were also used in characterizing the adsorption behavior of hydroxyl complexes of uranium. Interestingly, hydroxyl group on the uranium complexes showed slow sorption kinetics on the nanostructured silver surfaces. Understanding the adsorption behavior of aqueous solution of uranium on nanostructured silver surfaces has opened up the possibilities of SERS detection of these environmental and non-proliferation concerned species without any surface modifications. nTP is a high resolution printing technique and relies on interfacial chemistries to control the transfer of thin metal film from a "stamp" to a "substrate". In our research, high-aspect-ratio AutoCAD designed nanopatterns were created on silicon wafers using e-beam lithography and reactive ion etching. Silicon relief pillars based stamps were then used to integrate a variety of nanostructures on different dielectric materials. Thus created nanopatterns have shown their promise to hold their inherent SERS activity. For its simplicity, cost-effectiveness, and ease of operation, this hyphenated nTP-SERS technique is impressive in the selection of suitable supporting-films for better SERS enhancements and also to manipulate gap between nanodiscs (gap-plasmonic SERS effect).

Novel Electrochemical Detections Of Biologically And Environmentally Relevant Substances, Clarissa E. Tatum

Doctoral Dissertations

Development and studies of new electrochemical methods for the detection of various biologically and environmentally relevant substances are the focus of this dissertation. A dual amperometric sensor, capable of the simultaneous, real-time determination of NO and O,2, has been developed and optimized. Many tests were performed in order to reduce cross-talking between the two sensors, and an electro-deposited polymer, poly-5-amino-1-naphthol, was shown to reduce the cross-talking to insignificant levels. The use of bismuth-based electrodes in the detection of various metals has been explored. A bismuth bulk electrode has been developed, optimized, and used for the individual and simultaneous determination of …

Multidimensional Liquid Chromatography Separations, Jacob N. Fairchild

Doctoral Dissertations

Many mixtures important to research consist of hundreds or even thousands of individual components of interest. These types of mixtures are far too complex to separate by a single chromatographic dimension in any reasonable amount of time. However, if a multidimensional approach is used, where a complex mixture is separated by an initial dimension, simpler fractions of that separation are collected and each of those fractions are analyzed individually, highly complex mixtures can be resolved in relatively short amounts of time. This dissertation serves as a guide to multidimensional chromatography, in particular, two-dimension liquid chromatography. There are many aspects of …

New Electrochemical And Optical Detection Methods For Biological And Environmental Applications, Royce Nicholas Dansby-Sparks

Doctoral Dissertations

Detection of chromium and vanadium is of interest for biomedical and environmental applications. The two metals have narrow limits between being essential and toxic for humans. Ultra-sensitive techniques have been studied to measure Cr and V at low concentrations found in human blood and environmental samples. Bismuth film and mercury-alloy electrodes have been developed as alternatives to traditional Hg-based electrodes for Cr and V detection. While catalytic adsorptive stripping voltammetry (CAdSV) has been used to detect Cr and V, little is known about the process. The mechanisms of CAdSV have been probed to provide a better understanding of its exceptional …

Development Of Nanomechanical Sensors For Environmental Contaminate Screening Using Protein Functionalized Microcantilevers, Kasey L. Hill

Doctoral Dissertations

The development of real time, label-free biosensors based on ligand-induced nanomechanical responses of microcantilevers (MCs) allows for sensitive and selective detection. High sensitivity is afforded by the MCs small dimensions. Immobilizing biomolecular recognition phases imparts selectivity from bioaffinity interactions. Biological sensors on a MC platform utilize various proteins, such as antibodies and nuclear receptors, which can be used to detect and screen for potential environmental contaminants.

The interaction between contaminants and immobilized receptors induces an apparent surface stress that leads to static bending of the MC, which is monitored by an optical beam bending technique. Biofunctionalized MCs can provide high …

Radial Heterogeneity And Surface Properties Of Columns Used In High Performance Liquid Chromatography, Jude A. Abia

Doctoral Dissertations

The radial heterogeneity of some columns used in high performance liquid chromatography (HPLC) was investigated using an on-column microelectrochemical amperometric detector. Such a detector allowed the recording of the elution profiles at different spatial positions throughout the column exit cross-section. From this, we obtain information about the radial distribution of the mobile phase velocity, column efficiency, and analyte concentration. In all cases, the results obtained show that the spatial distribution of the mobile phase velocity does not follow a piston-flow behavior but exhibits radial heterogeneity with differences not exceeding 5% between the center and wall regions of any column. The …

Newly-Developed Nanostructured Microcantilever Arrays For Gas-Phase And Liquid-Phase Sensing, Zhou Long

Doctoral Dissertations

The microcantilever (MC) has become a common transducer for chemical and biological sensing in gas phase and liquid phase during recent years. MC sensors provide superior mass sensitivity by converting weak chemical and biological stimuli into high mechanical response. Moreover, other advantages such as small size, low cost and array format have made MCs more attractive than other comparable sensors.

Selectivity in MC sensors can be enhanced by creating a differentially functionalized MC array (MCA) with responsive phases (RPs). A well-designed array should incorporate RPs exhibiting a variety of possible interactions with the analytes, and a specific analyte should induce …

Classification And Fertility Of Soils In The Big South Fork National River And Recreation Area Based On Landscape Position And Geology, Ryan H. Blair

Masters Theses

The Big South Fork National River and Recreation Area encompasses more than 50,585 hectares (125,000 acres) of the Cumberland Plateau along the border of Tennessee and Kentucky. Highly dissected and steep terrain have made accessibility to much of the park limited, thus little work has been done to investigate the formation of these soils. Seven native soil profiles were selected for chemical and physical analysis representing Pennsylvanian-aged acidic sandstone and shale geology and landforms. The objectives of this study included the characterization of selected native profiles by physical and chemical analysis, as well as classification using US Soil Taxonomy, to …

Advancing Data Analysis For Spectroscopic Imaging By Combining Wavelet Compression With Chemometrics, Robert Daryl Luttrell

Doctoral Dissertations

Spectroscopic imaging is a vital tool for studying heterogeneous samples such as bacteria and tissue. Its ability to acquire spatially resolved information allows for identification and classification of the various constituents within a sample. Spectroscopic imagers quickly acquire thousands to tens of thousands of spectra per measurement. These data are often arranged in the form of a 3-dimensional (3D) data cube which contains two spatial dimensions and one spectral dimension. This large amount of data is beneficial for gaining a thorough understanding about the distributions of chemical information. If too little information is measured, important chemical behavior may be overlooked. …