Browsing College of Natural Science and Mathematics (CNSM) by Subject "Analytical chemistry"
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Bioanalytical Development Of Charged Cyclodextrin Capillary Electrokinetic Chromatography And Microperfusion Sampling To Study Endogenous D-Serine And L-Glutamate Efflux In BrainA multitude of studies have revealed specific biological mechanisms that contribute to D-amino acid action and regulation in the mammalian central nervous system. The remarkable increase in our understanding of D-amino acid function and distribution in mammals is in many ways a result of the development of sensitive enantioselective separation strategies that allow for quantification in real biological samples. In capillary electrokinetic chromatography (cEKC) the most powerful chiral resolving agents are anionic cyclodextrins (CDs), yet these have not previously been investigated for chiral bioanalysis of amino acids. The focus of this dissertation research was to investigate for the first time the feasibility of and application of anionic cyclodextrins as resolving agents in bioanalytical chiral separations of amino acids. This dissertation encompasses (1) the development of a new bioanalytical separation utilizing capillary electrophoresis laser induced fluorescence (CE-LIF) with sulfated-beta-cyclodextrin for analysis of D-serine (D-ser) and L-glutamate (L-glu) in mammalian brain, (2) the first synthesis and characterization of 6 members of a new family of single isomer sulfoalkyl cyclodextrins, (3) initial studies on chiral analysis of amino acids using single isomer sulfoalkyl CDs, and (4) development and application of a novel microperfusion sampling approach for acute brain slices and coupling of this method to the developed chiral CE-LIF for studying magnitude and timing of D-ser and L-glu efflux from acute hippocampus in response to modeled cerebral ischemia. The results of these studies demonstrate that (1) anionic CDs are powerful chiral selectors for amino acids and can be applied for sensitive bioanalysis of D-amino acids including D-ser, D-glu, and D-asp in brain samples; (2) single isomer sulfoalkyl CDs can be synthesized by regioselective reaction chemistry; (3) single isomer sulfoalkyl CDs are excellent resolving agents for amino acid analysis and may be valuable for bioanalytical chiral applications; and (4) microperfusion sampling coupled to CE-LIF can be used to analyze dynamic changes in the magnitude and timing of neurochemical efflux from single acute hippocampus slices exposed to modeled ischemia. Results of these latter studies suggest that D-ser and L-glu efflux occurs simultaneously in acute hippocampus with similar timing but differing magnitudes.
New instrumentation for the detection of sulfur dioxide in the remote atmosphereSulfur gases are an important chemical component of the atmosphere. Gaseous sulfur compounds effect the acidity of rainwater and are important precursors to aerosol particles which affect public health, climate and visibility of scenic vistas such as the Grand Canyon. Sulfate aerosols are also known to participate in ozone catalysis in the stratosphere. A vast majority of the gaseous sulfur cycling through the atmosphere will exist as sulfur dioxide (SO2) at some time during its atmospheric lifetime. Since SO 2 is a primary component of the atmospheric sulfur cycle, quality measurements of this gas are important to understanding the cycling of sulfur through the atmosphere. The mixing ratio of SO2 in the atmosphere can be as low as a few 10's of parts-per-trillion by volume (pptv) in unpolluted areas and as high as 100's of parts-per-billion by volume (ppbv) near industrial centers. Obtaining SO2 measurements with mixing ratios that can differ by 105 in magnitude is a difficult task, especially for mixing ratios less than a few hundred pptv. The Diffusion Denuder/Sulfur Chemiluminescence Detector (DD/SCD) was developed further and tested in a rigorously blind comparison under controlled laboratory conditions. The DD/SCD exhibited excellent sensitivity and little-to-no interference from other trace gases. The DD/SCD performance was comparable to that of other state-of-the-art instruments developed for measuring SO 2 in the remote atmosphere. The Continuous SO2 Detector was developed to overcome the limitation of long sampling times (4 to 90 minutes) inherent in the DD/SCD and other state-of-the-art techniques. The Continuous SO2 Detector (CSD) was developed based on the design of the DD/SCD, but has been optimized for sensitive, high-time resolved measurements of SO2 in air. Sensitive, high-time resolved measurements would be beneficial for studying atmospheric SO2 over large geographical areas from a moving sampling platform such as an aircraft. The current prototype of the CSD is capable of measuring SO2 at mixing ratios of less than 100 pptv on the order of seconds. The DD/SCD, CSD and an automated, computer controlled dynamic dilution system described in this thesis represent a suite of instruments for the measurement of SO2 in the remote atmosphere.
Nitrogen oxide photochemistry in high northern latitudes during springThe transport of NOy reservoir species from midlatitudes into the Arctic and the thermal and photochemical breakup of these species has been proposed to be the most important NOx source during spring, and may have an important influence on the ozone budget. This has not yet been shown to be correct. The objective of this research is to understand the sources of NOx and ozone in high latitudes during spring. To measure NOx, a high sensitivity chemiluminescence NO detector and a photolytic converter for NO$\sb2$ were constructed. The detection limits for NO and NO$\sb2$ were 1.70 and 5.67 part per trillion (pptv) in a one-hour average, respectively. Springtime NOx measurements were carried out concurrently with measurements of ozone, PAN, J(NO$\sb2$), and other species during 1994 at the Zeppelin station on Svalbard, and during 1993 and 1995 at Poker Flat, Alaska. The median mixing ratios of NOx, PAN and ozone at Svalbard were 23.7, 237.0 pptv, and 39.0 parts per billion (ppbv), respectively. During a few ozone depletion events in the Arctic marine boundary layer ozone and NOx mixing ratios were as low as 4 ppbv and 0.9 pptv, respectively. Halogen chemistry is probably responsible for both effects. The median NOx, PAN and ozone mixing ratios at Poker Flat were 79.5 pptv, 85.9 pptv, and 40.6 ppbv, respectively. During April and May diurnal cycles of PAN, ozone and temperature were observed and anticorrelated with the water mixing ratio. We interpret this to be the result of mixing with higher layers of the troposphere during the day. At both locations thermal PAN decomposition was an important NOx source. At Svalbard PAN decomposition was small, and the in-situ ozone production rates are an insignificant contribution to the ozone budget. Because of the higher temperatures, PAN decomposition rates, NOx mixing ratios, and in-situ ozone production rates are higher at Poker Flat. A contribution from this production to the overall ozone budget was visible during some periods. These results indicate that stable ozone precursors which are transported into the Arctic from anthropogenic sources can influence the ozone budget in high latitudes.
Oceanic emissions of sulfur: Application of new techniquesSulfur gases and aerosols are important in the atmosphere because they play major roles in acid rain, arctic haze, air pollution, and climate. Globally, man-made and natural sulfur emissions are comparable in magnitude. The major natural source is dimethyl sulfide (DMS) from the oceans, where it originates from the degradation of dimethysulfonioproprionate (DMSP), a compound produced by marine phytoplankton. Global budgets of natural sulfur emissions are uncertain because of (1) the uncertainty in the traditional method used to estimate DMS sea-to-air flux, and (2) the spatial and temporal variability of DMS sea-to-air flux. We have worked to lessen the uncertainty on both fronts. The commonly used method for estimating DMS sea-to-air flux is certain to a factor of two, at best. We used a novel instrumental technique to measure, for the first time, sulfur gas concentration fluctuations in the marine boundary layer. The measured concentration fluctuations were then used with two established micrometeorological techniques to estimate sea-to-air flux of sulfur. Both methods appear to be more accurate than the commonly used one. The analytical instrument we used in our studies shows potential as a direct flux measurement device. High primary productivity in high-latitude oceans suggests a potentially large DMS source from northern oceans. To begin to investigate this hypothesis, we have measured DMS in the air over northern oceans around Alaska. For integrating and extrapolating field measurements over larger areas and longer time periods, we have developed a model of DMS ocean mixing, biological production, and sea-to-air flux of DMS. The model's main utility is in gaining intuition on which parameters are most important to DMS sea-to-air flux. This information, along with a direct flux measurement capability, are crucial steps toward the long-term goal of remotely sensing DMS flux. A remote sensing approach will mitigate the problems of spatial and temporal variability. The new developments in methodology, field sampling, and modeling put forth in this thesis are tools we have used to better understand and quantify sulfur gas emissions from northern oceans, which appear to be a significant source of sulfur to the global atmosphere.