Understanding Atmospheric Aerosol Dynamics and Condensed-Phase Chemistry via Laboratory-Based Aerosol Mass Spectrometry (AMS)

Niedek, Christopher University of California, Davis ProQuest Dissertat 2025 해외박사(DDOD)

Organic aerosols, and atmospheric condensed phases more broadly, are important components of the troposphere. Despite a large amount of effort over the past few decades to better understand the dynamic chemistry of ambient aerosols, our knowledge of the characterization and fate atmospheric condensed-phase species remains limited. A critically understudied aspect of this chemistry is the chemical processes occurring in aqueous particles and aerosol liquid water (ALW). A more thorough characterization of the chemical composition and processes of these atmospheric condensed phases is necessary to improve the accuracy of models of aerosol impacts on climate change and human health. This dissertation focuses on developing novel methodologies for the study of atmospheric condensed phases and applying these techniques to understand the aqueous-phase chemistry of phenols and furans (both important biomass burning (BB) emission species) under more ALW-like conditions and to examine vertical distributions in ambient aerosol chemistry.Chapter 2 presents a unique application of lab-based, analytical aerosol chemistry techniques to evaluate the ability of purported "aerosol barriers" to retain aerosols in a hospital setting. Shortly after the start of the COVID-19 pandemic, there was interest in the use of various types of barrier devices to protect hospital staff from potentially infectious respiratory aerosols during aerosol generating procedures (e.g. intubation). However, very little data existed on the ability of these types of devices to retain aerosols and therefore protect the user. A novel methodology involving simultaneous, real-time analysis of modeled, exhaled particles using an aerosol mass spectrometer (AMS) and condensation particle counter (CPC) was developed to evaluate the aerosol retention characteristics of barrier devices. Aerosol retention was largely dependent on the degree of enclosure of the barrier device. A barrier device that fully encloses a patient can effectively retain respiratory aerosols, while aerosols could be detected leaking from any available opening. Additionally, aerosol evacuation can be performed to reduce the internal aerosol count to near-background levels.Chapter 3 details the development of a micronebulization aerosol mass spectrometry (MN-AMS) technique for analysis of low volume, low dissolved mass extracts of particulate matter (PM) collected on filters. Limitations on standard filter extraction and aerosol generation techniques require long filter collection times and prohibit the use of advanced PM collection strategies like uncrewed aerial systems (UAS). The MN-AMS technique can generate aerosols suitable for AMS analysis from microliter volumes of liquid filter extracts containing nanograms of dissolved PM, a significant improvement over standard aerosol generation techniques. This technique was evaluated against standard aerosol generation techniques with the AMS and ion chromatography and was able to accurately reproduce expected aerosol chemical compositions across a range of solution volumes. Then, samples collected on the ground and aboard a UAS at the Southern Great Plains (SGP) atmospheric observatory Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) user facility were analyzed using MN-AMS. This technique accurately reproduced the expected aerosol chemical compositions and mass concentrations ascertained by on-the-ground measurements performed by an aerosol chemical speciation monitor (ACSM). Chapter 4 further demonstrates the MN-AMS technique by examining the detailed chemistry of a set of filter samples collected using the ARM UAS named the ArcticShark during a set of flight campaigns performed in March, June, and August of 2023. On-board measurements of ambient RH, temperature, wind speed and direction, and cloud droplet concentrations were combined with ground-based measurements of cloud-base heights and planetary boundary layer heights (PLBH) to better understand aerosol chemistry at SGP both at ground level and aloft. Chemistry measured at altitude was compared to a ground-level ACSM. The two measurements were most similar when the PBLH was high and the ArcticShark was sampling well below it. When the ArcticShark had significant sampling time above the PBL, measurements of PM chemistry diverged from those measured on the ground. Additionally, seasonal insights into PM chemistry at SGP, including seasonal variations in organic nitrogen species, were discussed. Both the speciation and average oxidation state of organic nitrogen species changes from March and June to August. Last, positive matrix factorization (PMF) was applied to the UAS samples on a monthly basis. In each month, factors similar to oxidized organic aerosols (OOA) were found. In March and June, a factor was found that correlated to specific samples that were largely from above the PBL and resembled highly oxidized (relative to the rest of the monthly samples) OA that was chemically distinct from PM measured during the other sampling days in March and June.In Chapter 5, a novel photoreaction system named the small pathlength photoreactor (SPP) is described. The SPP was designed to study condensed-phase photochemistry at conditions similar to those found in ALW. General characterization of the SPP was performed, including RH and temperature control within the reaction chamber and comparison of model reactions of phenol and furan photochemistry performed in more established photoreaction systems. Photochemistry under ALW conditions was exemplified by examining guaiacyl acetone (GA), a model BB phenol, and 3,4-dimethoxybenzaldehyde (DMB), a model triplet carbon photosensitizer, photochemistry under high organic concentrations and high salt concentrations. High concentrations of light absorbing organics can cause issues with light screening under typical photochemical setups where pathlengths are on the order of 1 cm. GA decay rates are notably increased as DMB concentrations increase, even despite light screening caused by increased GA concentrations, and high salt concentrations cause a slight decrease in GA decay rates. Similarly, the rate of GA oligomerization is increased under high organic concentrations and decreased under high salt conditions. Secondary organic aerosol yields are generally decreased under ALW conditions.In Chapter 6, the SPP is further utilized to examine furan-singlet oxygen (1O2) under high ionic strength conditions. Like phenols, furans can be significant components of BB emissions. Singlet oxygen chemistry has been explored in environmental waters, and under low salt concentration (<2 M) conditions, but almost no data exists on 1O2 chemistry under ALW conditions where ionic strengths can reach as high as 20 M, at least an order of magnitude higher than what has been studied prior. For reactions of FFA and 1O2 (generated from rose Bengal (RB), a common 1O2 photosensitizer), a moderate correlation between photosensitizer absorption area and FFA decay rate was found. This suggests that ionic strength is modifying the 1O2 steady-state concentration of the system, as opposed to second order rate constants between furans and 1O2. The effects of ionic strength on the furan-1O2 were also explored more broadly by examining the decay rates of a set of furans using different 1O2 photosensitizers and salts. Similar to what has been shown in the literature under low ionic strength conditions, ionic strength effects on 1O2 photochemistry are highly dependent on salt concentration, salt identity, 1O2 photosensitizer identity, and to a lesser extent the identity of the furan. Singlet oxygen photosensitizer identity seems to be the largest contributor, where different photosensitizers exist in different regimes of salt effects on furan-1O2 chemistry.

Raman investigations on high pressure phases of carbon based novel networks

Trout, Chad Christopher The Pennsylvania State University 2001 해외박사(DDOD)

Solid-state chemistry plays an important part in everyday life, from the material that coats the blade of your razor to the way your refrigerator keeps cool. The search for new and interesting materials is a broad and exciting area of solid-state chemistry. Carbon plays a large role in life and in solid-state chemistry. Carbon's versatility in bonding gives its compounds various physical, chemical, and biological properties. The versatility of carbon comes from the ability to form novel covalent networks containing sp, sp<super>2</super> and sp<super>3</super> bonds. These networks can exhibit a wide variety of structures and properties. The composition of amorphous carbon can range from only sp<super>2</super> carbon to various amounts of sp<super>2</super> and sp<super>3</super> carbon giving a variety of properties. In the last two decades, several new forms of carbon have been discovered, reopening the interest in carbon chemistry. There is still much to learn about solid-state carbon chemistry. Two aspects of solid-state chemistry are addressed in this thesis. The first aspect, is chemists' ability to make an educated guess about reaction pathways. The pathways of organic reactions are often understood, which allows organic chemists to make educated guesses about these reaction pathways. In solid-state chemistry there is a lack of understanding of the pathways for the reactions to proceed. In topochemical reactions the crystal structure of the monomer controls the final product and a crystal is formed. With these types of reactions a crystal is obtained instead of the usual amorphous or mixed phase material. The crystal's structure can be determined, which can lead investigators to determine the reaction pathway. Together topochemcial reactions may shed light on other reactions. The improved characterization of solid-state carbon materials is investigated in this work. Towards that respect, ultra violet (UV) Raman spectroscopy is being used for the first time on carbon based materials synthesized in the diamond anvil cell. Visible Raman spectroscopy often gives little or no information when dealing with amorphous phases of carbon based materials. This is due to the resonance enhancement of sp<super>2</super> carbon bonds with visible Raman spectroscopy. This resonance enhancement hides other features, such as carbon and nitrogen bonds in carbon nitrides and sp<super>3</super> carbon bonds in amorphous carbon. Previously, materials such as carbon nitrides were synthesized and investigated with other analytical methods. UV Raman spectroscopy allows new features in carbon based networks to be observed that were not detected with the other analytical methods. Vibration modes associated with sp<super>3</super>-boned carbon and nitrogen can be observed, indicating that new covalent networks of carbon and nitrogen have been synthesized. UV Raman is a relatively new technique and has not been applied to diamond anvil cell work previously. Various diamonds were investigated for in situ reactions in the diamond anvil cell with UV. Investigations were also performed on materials synthesized in the diamond anvil cell and then quenched to atmospheric pressure. These quenched samples were then studied with UV Raman.

Relative Quantification of N-linked Glycans in Complex Mixtures via Stable Isotope Labeling and Enhanced Analysis by Liquid Chromatography Coupled Online to Mass Spectrometry

Walker, Steven Hunter North Carolina State University 2013 해외박사(DDOD)

Glycomics is a rapidly emerging field due to the ubiquity and functional importance of glycosylation in biological systems. However, the current analytical tools for studying glycomics and glycoproteomics lag decades behind proteomics and, to a larger degree, genomics. Additionally, the increasing advancements in separations and mass spectrometry technology (e.g. the Orbitrap) are not being fully taken advantage of due to the lack of reproducible, robust, and high-throughput front-end glycomics sample preparation strategies. Thus, this dissertation describes an effort to develop a high-throughput chemical derivatization strategy for the relative quantification of N-linked glycans, which can be coupled to nearly any glycomics sample preparation procedure with minimal monetary and time cost. The motivation for this work is the correlation between aberrations in glycosylation and disease. Thus, a strategy capable of systematically comparing and quantifying glycan profiles between samples (e.g. control and cancer samples) would be invaluable in glycan biomarker discovery efforts. Additionally, this work has been primarily developed in the most complex of biological matrices, blood plasma. There are two main reasons for this: 1) because plasma is one of the most complex matrices, it is likely that this technique will be effective when applied to any other biological matrix, and 2) plasma samples can be acquired without invasive surgery. This means that a screening method derived from biomarkers discovered in plasma will ultimately be inexpensive and non-invasive in practice. Aside from the possible clinical value of this quantification strategy, this work has made significant contributions to the field of glycomics and fundamental analytical chemistry including both experimental and practical advantages. By developing tunable glycan reagents, it has been shown that these tags are capable of both relatively quantifying N-linked glycans and systematically decreasing the detection limits of N-linked glycans in plasma samples using mass spectrometry. Because glycomics strategies often involve numerous sample preparation steps, the addition of chemical derivatization typically only further complicates the preparation. However, the strategy presented herein requires only 4 hours of total additional sample preparation time (samples can be processed in parallel), and the reaction products can be immediately analyzed. This is a significant advantage over traditional glycan derivatization strategies such as permethylation and reductive amination. Finally, this work has also contributed to the fundamentals of analytical chemistry and, more specifically, mass spectrometry. By tuning the glycan reagents with different functional properties, the mechanism for the generation of gas phase ions in electrospray ionization was able to be studied, and using these results, biases in the electrospray process were able to be exploited for the enhanced detection of glycans by mass spectrometry. Furthermore, liquid chromatography of glycans is often coupled online to mass spectrometry for the separation of glycans just before mass analysis, and traditionally, glycans are not able to be retained and separated using reverse phase chromatography (the most robust separation strategy for biological analytes). However, using the reagents developed and presented herein, the separation of glycans by reverse phase liquid chromatography is not only possible, but it is advantageous, allowing for increased separation efficiency and an increase in the total number of glycans detected. A significant practical advantage of this strategy is the ability to analyze glycan samples on the same instrument platform as a majority of proteomic strategies. This significantly increases the efficiency of joint proteomic and glycomic laboratories and facilitates a more comprehensive systems biology approach to bioanalytical chemistry.

The use of stable isotopes and particulate matter in the investigation of local and regional atmospheric chemistry

Katzman, Tanya Lynn Purdue University ProQuest Dissertations & Theses 2016 해외박사(DDOD)

The chemical composition of particulate matter (PM), a known contributor to air pollution, is highly variable, and elemental analysis reveals information about local and regional sources, as well as how air masses and climate influence PM compositions. Seasonal changes in climate, such as temperature, amount of daylight, or meteorological patterns influence source emissions (increased residential heating activities, decreased natural soil emissions) and the relative importance of certain chemical pathways in the atmosphere. Since the magnitude of these seasonal changes are highly dependent on location, each sampling site is unique and the chemical composition of PM provides valuable insight into local and regional atmospheric chemistry. Elemental analysis was used to evaluate local atmospheric chemistry at four sites in Southern California (Chula Vista, El Cajon, El Centro, and Brawley) and in Whangarei, New Zealand. PM in Southern California sites revealed seasonal trends, but also how emissions from the 2007 wildfire season impacted local chemistry, producing elevated PM and trace gas concentrations and low O3 concentrations. Analysis of PM collected in Whangarei, New Zealand revealed that local atmospheric chemistry is heavily influenced by marine air masses, seasonal shifts in source contributions (e.g. residential heating activities), and changes in boundary layer height. Stable isotope ratios are often applied as tracers of sources and local chemistry, which is extremely useful for deciphering PM. As the main NO x sink, the stable isotope composition of NO3- reflects NOx sources contributions, oxidation pathways, and other processes that effect the isotope distribution (e.g. equilibrium exchange). However, the use of N isotopes (delta15N) as a tracer is usually split between two schools of thought: the source hypothesis and the chemistry hypothesis. The source hypothesis claims that the delta 15N value of NO3- is solely determined by NOx source delta15N values, and observed variations are due to shifts in source emissions. Alternatively, the chemistry hypothesis argues that the delta15N value of NO3- is impacted by source contributions and chemical reactions occurring in the atmosphere. Here, variations in observed delta15N values are attributed to changes in reaction pathway contribution, as well as shifts in source emissions. Stable isotope analysis of NO3- collected in Southern California and Whangarei, New Zealand was used to evaluate these hypotheses. Using source emission data, known delta15N values of NOx sources, and observed delta15N values of NO3- collected in Chula Vista, CA, isotope mass balance suggests that the source delta15N value is not conserved, requiring a NOx source with an unreasonably large delta 15N value (~ 280‰) to explain observed values. Isotope exchange equilibrium was found to explain observed delta15N values well, but deviations did exist, particularly in the winter. These deviations are likely due to shifts in the importance of this exchange and additional fractionation effects associated with reaction pathways. Additionally, the inverse correlation between delta15N and solar radiation observed in Whangarei further supports the chemistry hypothesis. The research presented in this dissertation is the first known evaluation of these two stable isotope hypotheses, with the results strongly support the chemistry hypothesis. While the oxidation of NO2 is well understood, the mechanism of the oxidation of NO to NO2 is highly uncertain, and so stable isotopes were utilized to determine this reaction mechanism. Laboratory studies found that the remaining O2 became depleted relative to the O2, and followed a strict mass dependent relationship. Complimented by kinetic modeling, results strongly suggest that this reaction proceeds in two steps, with the formation of a peroxynitrate intermediate being favored due to the observed mass dependent relationship. This research is the first to offer support to the peroxynitrate intermediate, whereas previous works favored the energetically more stable nitrogen trioxide form.

Transport-kinetic processes and surface chemistry in biosensor design

Vijayendran, Ravi Albert University of Illinois at Urbana-Champaign 2001 해외박사(DDOD)

Biosensors are analytical devices that detect a target analyte on the basis of biomolecular recognition. Detection occurs as the consequence of specific interactions between the analyte and complementary biomolecules immobilized on the transducer surface. Several physicochemical factors influence this detection process. This thesis examines the role of these factors in sensor operation and also evaluates specific methods to manipulate these factors and improve sensor performance. We begin by investigating the kinetic and transport processes that underlie analyte recognition. A transport-kinetic model is developed to quantitatively relate these processes to sensor response in a typical biosensor measurement. Predictions from our model are compared with kinetic data from a fiber optic immunosensor. With these experimental comparisons, we demonstrate that our model provides a more physically rigorous description of analyte transport, and is thus better for data analysis and sensor design than competing models. The role of surface effects in biosensor operation is also addressed. We examine how immobilization impacts the activity of the biomolecules on the transducer surface. Although these molecules display homogeneous binding characteristics in solution, they often exhibit heterogeneous binding properties after surface immobilization. We measure binding isotherms and the detection kinetics for several analyte-receptor systems constructed with various immobilization strategies. By comparing theoretical models with experimental data, we elucidate the relationship between protein immobilization chemistry and receptor heterogeneity, and identify methods for constructing more uniformly reactive protein films. Finally, sample mixing is examined as a potential method to improve the performance of microfluidic biosensors. We attempt to mix sections of the sample solution where the analyte concentration is high with other sections where it is low, and thereby reduce the sensor response time when the detection kinetics are diffusion-limited. A serpentine micromixer, originally designed to mix two fluids in bulk solution via “chaotic advection,” is used to mix the sample as it passes through a surface plasmon resonance biosensor. These experiments indicate that such “solution-based” mixing strategies can be effective in microfluidic biosensors.

Surface-Enhanced Raman Spectroscopy of Analytes in Blood

Campos, Antonio Renteria, II University of Minnesota 2015 해외박사(DDOD)

Although Raman scattering has traditionally been considered a weak process, making analysis of low concentration analytes in complex matrices difficult, both methodological and instrumentation advances in the last couple decades have made Raman spectroscopy a viable and useful analytical tool. This is especially true for analyte species within aqueous environments because the Raman scattering cross-section of water is small; one particular example of a critical aqueous environment is analysis of and in blood. The work detailed in Chapter 1 will analyze much of the literature related to Raman analysis in blood within the last 20 years, including normal Raman, surface-enhanced Raman, and spatially offset Raman analyses. The first section will focus on direct analysis of blood samples, including determining the age of deposited or donated blood and blood content within body fluid mixtures. The second section will discuss intrinsic Raman-based detection of small molecules and protein analytes within blood as well as extrinsic Raman detection of tumors. The last section will review the recent use of spatially offset Raman and surface-enhanced spatially offset Raman spectroscopy to analyze molecular analytes, tissue, bone, tumors, and calcifications, including in vivo analysis. This focal point closes with perspective on critical gaps and upcoming developments for Raman analysis in blood. Raman detection in blood can be applied to different forensic fields and can also be used for the detection of foreign analytes. In current events, ricin has been discussed frequently because of letters sent to high-ranking government officials containing the easily extracted protein native to castor beans. Ricin B chain, commercially available and not dangerous when separated from the A chain, enables development of ricin sensors while minimizing the hazards of working with a bioterror agent that does not have a known antidote. As the risk of ricin exposure, common for soldiers, becomes increasingly common for civilians, there is a need for a rapid, real-time detection of ricin. To this end, aptamers have been used recently as an affinity agent to enable the detection of ricin in food products via surface-enhanced Raman spectroscopy (SERS) on colloidal substrates. One goal of this work is to extend ricin sensing into whole human blood; this goal required application of a commonly used plasmonic surface, the silver film-over-nanosphere (AgFON) substrate, which offers SERS enhancement factors of 106 in whole human blood for up to 10 days. This aptamer-conjugated AgFON platform enabled ricin B chain detection for up to 10 days in whole human blood. Principle component analysis (PCA) of the SERS data clearly identifies the presence or absence of physiologically relevant concentrations of ricin B chain in blood. In addition to the detection of ricin B chain at a relevant concentration, the development of a platform to perform a single experiment calibration curve was performed through the combination of microfluidic devices with SERS substrates. Microfluidic sensing platforms facilitate parallel, low sample volume detection using various optical signal transduction mechanisms. Herein, we introduce a simple mixing microfluidic device, enabling serial dilution of introduced analyte solution that terminates in five discrete sensing elements. We demonstrate the utility of this device with on-chip fluorescence and surface-enhanced Raman scattering (SERS) detection of analytes, and we demonstrate device use both when combined with a traditional inflexible SERS substrate and with SERS-active nanoparticles that are directly incorporated into microfluidic channels to create a flexible SERS platform. The results indicate, with varying sensitivities, that either flexible or inflexible devices can be easily used to create a calibration curve and perform a limit of detection study with a single experiment. In Chapter 4, the synthesis of an ultrastable and reversible pH nanosensor using gold nanosphere aggregates functionalized with 4-mercaptobenzoic acid (MBA) that are encapsulated in mesoporous silica was performed. The pH nanosensor is stable and functional in human whole blood for a period of more than 3 months. With the growing interest in nanoparticles and nanomaterials, a demonstration was organized for a high school AP Chemistry class. Spectrophotometry and colorimetry experiments are common in high school and college chemistry courses. Previous work has demonstrated that handheld camera devices can be used to quantify the concentration of a colored analyte in solution in place of traditional spectrophotometric or colorimetric equipment. Chapter 5 extends this approach to an investigation of a mesogold mineral supplement. With the addition of free Google applications, the investigation provides a feasible, sophisticated lab experience, especially for teachers with limited budgets.

Utilizing the Properties of Functional Groups to Understand Indoor, High NOx, and Low NOx Atmospheric Chemistry

Ziola, Anna C University of Colorado at Boulder ProQuest Dissert 2024 해외박사(DDOD)

Over 1000 Tg of volatile organic compounds (VOCs) are emitted into the atmosphere every year from both biogenic (Guenther et al., 2012) and anthropogenic (Huang et al., 2023) sources, an equivalent weight of about 200,000 school buses per day. Depending on the structure of these compounds and conditions in which they exist, they can remain in the atmosphere for seconds to years. This thesis investigates the fate of selected volatile organic compounds in three types of conditions: low NOx, high NOx, and indoor environments.The first study was inspired by the significant decrease of nitrogen oxides (NOx) in the U.S. in the last few decades. This reduction has led to the oxidation of VOCs - crucial for the formation of ozone and fine particles - occurring in urban areas under conditions historically associated with remote rural locations. To gain a better understanding of VOC oxidation mechanisms, I investigated the fate of two model linear alkenes that were chosen due to the high abundance of alkenes in atmospheric emissions and the simplicity of the selected compounds. By reacting 1-pentene and 3-butenoic acid with OH radicals in an environmental chamber under low NOx conditions, monitoring the gas- and particle-phase products (and 3-butenoic acid) using real-time mass spectrometry and offline techniques, and kinetics modeling, I was able to elucidate the oxidation mechanisms of these compounds. This allowed for a better understanding of the effect of a carboxyl group on reaction branching ratios and product yields.In the second study, I investigated the OH radical-initiated oxidation of a model ether compound under high NOx conditions. Ether groups are commonly found in more functionalized volatile chemical products (VCPs) - anthropogenic sources of VOCs that come from cleaning products, personal care products, adhesives, and elsewhere (Seltzer et al., 2021). Although it is known that ether groups affect reaction kinetics, nitrate yields, and SOA yields, the mechanism and degree to which a single ether group impacts the products formed from a large ether has not been determined or quantified. Therefore, for this study I reacted dioctyl ether (a symmetric C16 compound with a central ether group) with OH radicals under high NOx conditions; identified and quantified the gas- and particle-phase products using mass spectrometry, gas chromatography, liquid chromatography, and spectrophotometric techniques; and developed a quantitative reaction mechanism to explain their formation which could be used in models.In the final chapter I investigated the fate of carboxylic acids and ozone in simulated indoor conditions. Humans spend the majority of their life indoors, yet we have limited knowledge about the chemistry that occurs in these spaces. One major process that impacts the composition of indoor air is surface chemistry. Indoor spaces can have dozens of different surfaces, each with unique properties and compositions. Here, I investigated the mechanisms by which carboxylic acids and ozone interact with various wood species and wood coatings, including lacquer and shellac. An iodide chemical ionization mass spectrometer (I-CIMS) and ozone monitor were used to measure uptake coefficients and deposition velocities in uncoated and coated tubes, an attenuated total reflectance-Fourier transform infrared spectrometer was used to measure diffusion coefficients of carboxylic acids in wood and coatings, and a multi-layer model was used to extract compound diffusion coefficients and material absorbance capacities from experiments. The results were then used to develop a conceptual model for describing the interactions of carboxylic acids wood and coatings.

Developing analytical methodologies for combinatorial chemistry using time-of-flight secondary ion mass spectrometry

Xu, Jiyun The Pennsylvania State University 2003 해외박사(DDOD)

In this thesis, imaging time-of-flight secondary ion mass spectrometry (ToF-SIMS) is applied to the high-throughput analysis of combinatorially synthesized organic molecules, which are normally referred to as libraries. Two issues need to be addressed for a library: the occurrence and structure of the library components and their bioactivity toward certain targets. Since bioassay can be rapidly handled with a variety of strategies, here we focus on identifying the library members using mass spectrometric methodologies. We establish parallel analysis protocols for combinatorial libraries synthesized both in solution phase and on solid phase, such as polymer resin particles. By acquiring molecule-specific images of the analytes densely arrayed either in picoliter-volume silicon vials for liquid samples or on arraying chips for polymer beads, analysis rates of 10 analytes/second on model systems has been achieved with imaging ToF-SIMS. The challenges lie in the development of appropriate treatments for diverse samples or samples presented in complex matrixes. For liquid samples, glass substrates modified with functional groups are employed to separate the analytes from a mixture solution through selective binding. As a result, SIMS sensitivity is greatly enhanced. Solid-bound libraries comprise of an intricate system because of the wide varieties of linker moieties and polymer matrixes involved in the synthesis. We examined the influence of three classes of linkers—acid or base labile linkers, a thermally labile linker and a photochemically cleavable linker, all of which are used to anchor one end of the analyte to the polymer resin. With data obtained using both SIMS, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM), we conclude that an effective treatment of the resin needs to include cleaving the linker and extracting the unbound analyte to the resin surface. We also demonstrate that the hydrophilicity of the polymeric constituents of a resin particle affects the experiments by changing the location of the analyte molecules during resin treatment. In addition, the spatial localization of the released analytes could be controlled by introducing a hydrophobic supporting substrate such as Teflon tape that confines the diffusion of the cleaving reagent. Encoding a library with tags is necessary when direct mass analysis fails to yield conclusive results due to mass redundancy and inadequate sensitivity. Two different encoding strategies and corresponding tags are designed, synthesized and examined with imaging ToF-SIMS. The dual recursive deconvolution (DRED) strategy differentiates the resins based on the varying concentrations of bromine and chlorine-derivatized polystyrene in their polymer matrixes. The resins are subsequentially decoded using isotopic signal intensities measured with SIMS. This scheme obviates the need for extra synthetic steps and cleaving reactions, thus is highly compatible with high-throughput analysis using imaging ToF-SIMS. (Abstract shortened by UMI.).

Advances in Instrumentation and Chemometrics of Two-Dimensional Gas Chromatography Systems

Mikaliunaite, Lina University of Washington ProQuest Dissertations & 2024 해외박사(DDOD)

Comprehensive two-dimensional (2D) gas chromatography (GCxGC) has gained significant popularity as an analysis tool for complex samples in metabolomics, petroleum science, and other fields. GCxGC has been shown to perform better than one-dimensional GC, including a 10-fold increase in peak capacity and more chemical selectivity. The work presented herein focuses on two aspects of GCxGC systems: advancements in instrumentation and chemometrics. While GCxGC is used to analyze volatile compounds, when it comes to very light analytes, like permanent gasses, new instrumental designs are needed, as widely applied wall coated open tubular (WCOT) columns do not work well. Also, thermal modulators, which are in most commercially available instruments, cannot trap such low boiling point analytes due to temperature limitations. Porous layer open tubular (PLOT) columns and flow modulators must be used for such samples. However, PLOT columns are not widely used in GCxGC due to their extreme retention on analytes, and hence being hard to pair with WCOT columns due to temperature differences that are needed for analytes to elute. In this work, we present a new GCxGC system with a PLOT column in the first dimension and a WCOT column in the second dimension. This system also used a high temperature diaphragm valve as a modulator. We showed the ability of this system to separate heavy mixtures like gasoline, and by trying thinner film PLOT columns, we showed the potential of this system to be used with even higher boiling point analytes.GCxGC is an essential analytical technique for biological samples, as they are complex and make a perfect sample for this technique. However, due to the biological variation that is possible in these samples, data analysis can be tricky. Here, we present three projects that analyzed biological samples: cycling yeast, moisture-damaged beans, and VOCs of Malassezia pachydermatis. While all were very different, they were analyzed using the tile-based Fisher ratio and then post-processed to answer specific biological questions of the dataset. When analyzing cycling yeast, we were looking for analytes that were not only changing between different classes but also had a specific cycling pattern. This was achieved by simulating random data to analyze which analytes were like random patterns and which had some underlying biological information. The second dataset presented is moisture-damaged cacao beans, where the F-ratio method had to be altered, so not only the analytes that were changing with the molding process would be found, but also the hits that were bean origin-specific and did not change with molding. Lastly, we analyzed VOCs produced by M. pachydermatis, when grown at three different pH. In this case, the analytes need to be classified into different types, based on how much and how they changed in signal between blank media and M. pachydermatis, and to be analyzed for potential pH-dependency. This was performed by post-processing using R-metric and RSD-metric.

SERS-based sensing platforms: Multilayer thin films, anisotropic nanoparticles, and core-shell structures

Mulvaney, Shawn Patrick The Pennsylvania State University 2001 해외박사(DDOD)

A technique capable of both qualitative and quantitative detection is Raman spectroscopy. Large enhancements in Raman scattering intensity can be realized when the analyte is in close proximity (<20 Å) to an appropriately roughened, noble metal surface. When analytes are examined in such a position the technique is known as surface enhanced Raman scattering (SERS), and enhancements as high as 10<super>14</super> have been reported. This thesis examines the improvement of SERS substrate performance. The second and third chapters describe the preparation and application of a multilayer metal film as a substrate for SERS. A novel substrate architecture was created by evaporating a discontinuous film of Ag over an Ag-clad colloidal Au submonolayer. This solid support substrate has an enhancement of 2 × 10<super> 6</super> and better than 15% reproducibility in signal. Analytes in more complex sample matrices can be examined when a thin film of polydimethyl siloxane (PDMS) is spin coated over the substrate. The PDMS film acts as a solid phase microextraction (SPME) medium, thereby concentrating hydrophobic analyte molecules near the SERS-active surface. Analytes positioned between two metal surfaces have enlarged Raman scatting because the signal is modulated by both metal surfaces. Chapter 4 addresses the deterministic preparation of these geometries, known as SERS sandwiches, that will be suitable for detailed study. Au-Ag-Au, rod-shaped nanoparticles can be prepared by membrane templated electrodeposition. Once these nanoparticles are immobilized on a surface the Ag strip can be etched leaving a closely space two particle surface feature. Details of preparing suitable films for the study of SERS sandwiches are reported. The final chapter describes the development of a SERS-active, core-shell particle to be used as a tagging system in bioassays. Glass-coated, analyte-tagged nanoparticles (GANs) are core-shell structures where a nanometer scale Au or Ag core is functionalized with a Raman active molecule and encapsulated in a glass shell. GANs particles are identified by the Raman spectrum of the attached Raman-tag. Scattering from that Raman-tag is amplified through SERS. Furthermore, biorecognition chemistry (i.e. nucleic acids, antibodies, antigens) can be attached to the glass shell without interfering with the Raman response.