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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Speciation of selenoamino acids and selenium compounds by GC-AED and HPLC-ICP-MS

Totoe, Harriet 01 January 2004 (has links)
The increasing demands for speciation in nutrition, clinical chemistry and toxicology have made the sole determination of the total element in a sample unsatisfactory. It is important to determine the chemical form (species) of the element; most often its oxidation state or its organometallic or complexed nature, since different species of the same element can range from harmless to essential to toxic. In order to address this challenge, a separation technique (gas chromatography, GC) that usually focuses on qualitative analysis was effectively interfaced with an element specific detection technique, atomic emission spectrometry (AED). Likewise liquid chromatography (HPLC) was interfaced to inductively coupled plasma mass spectrometry (ICP-MS) for the characterization of selenium compounds. The consumption of selenium nutritional supplements has been reported to provide anticarcinogenic benefits that are selenium compound dependent. The separation and identification of these selenium species is important in order to understand their activity and metabolism. In this study, methods were developed for the characterization of selenium species in selenized yeast, breath and urine samples. Enzymatic digestion of selenized-yeast samples followed by ethylchloroformate derivatization was used to dissolve amino acids and convert them to volatile compounds suitable for subsequent GC analysis. Volatile selenium species exhaled in breath were trapped on Tenax, then revolatilized by heating and sampled by solid phase microextraction. Gas chromatography with atomic emission detection (GC-AED) or gas chromatography with mass spectrometry (GC-MS) was employed for their detection. Selenium species in urine were characterized by ion-pair chromatography with ICP-MS detection. The monitoring of chromatographic eluents with element specific atomic spectroscopy detectors enabled the determination of selenium species in the enzymatic digests of selenized yeast, breath and urine samples. The analysis of archived selenized yeast samples by GC-AED and GC-MS revealed the presence of a previously unknown aminoacid, S-(methylseleno)cysteine. Low molecular weight organoselenium and mixed organosulfur-organoselenium compounds were identified by GC-AED in exhaled human breath samples from volunteers taking selenium nutritional supplements. Trimethylselenonium ion was identified in the urine of these volunteers by HPLC-ICP-MS.

Capillary electrophoresis-inductively coupled plasma-mass spectrometry in macromolecular characterization

Danku, John M. C 01 January 2006 (has links)
Interaction of metal ions, both essential and toxic, with macromolecules is important in biological and environmental systems. The availability of trace metals may govern an organism's nutritional strategy in a given environment. Metal ions are rarely found free in most systems because of their active nature. The transportation of contaminants and nutritionally important metal ions in the environment is facilitated by their ability to bind and form complexes with humic substances and other ligands. Capillary electrophoresis-inductively coupled plasma mass-spectrometry (CE-ICP-MS) has been explored to characterize metal ions bound to various macromolecules because of the rapid separation coupled with high separation efficiency, resolving power and small sample size requirements together with sensitive elemental detection capability afforded by this hyphenated technique. Macromolecules examined here include humic substances, selenium compounds and selenoproteins, and some metal transport and storage proteins. Characterization of metal ion complexed humic substances by CE-ICP-MS is a formidable analytical challenge. Particularly of concern are the potential interactions with the CE capillary wall and the poor concentration detection limit inherent with the CE technique. Thus, sample preconcentration by flow field-flow fractionation was employed. Addition of zwitterions to the separation buffer helped to alleviate analyte-capillary wall interactions. A case study of trace metals bound to soil humic acids (HAs) that were successively extracted from the slopes of a local mountain was performed using the developed method. Trace metals complexed with HAs declined with diminishing oxygen-rich moieties in the HA structure. Analysis of selenoproteins extracted from yeast and selenium-containing compounds obtained from selenized supplement tablets by CE-ICP-MS were investigated. It was demonstrated that bare CE capillaries coupled to ICP-MS are suitable for speciation analysis of low molecular weight selenium compounds using a cationic surfactant separation buffer modifier. However, baseline resolution was not always achieved for selenoproteins owing to analyte adsorption onto the capillary wall. Likewise, speciation of some storage and transport proteins had been carried out with uncoated capillary CE-ICP-MS. Very high concentrations of the samples were employed because of low signal sensitivity. Improvement of the interface is necessary in order for kinetic and binding studies to be attempted.

Selenium speciation in environmental and clinical samples

Hernandez, Princess C 01 January 2006 (has links)
Methods for selenium speciation using chromatographic and atomic spectrometric methods were developed. The objectives of the study were to quantify low concentrations of selenium and identify the different Se species present in some clinical and environmental samples. A 10 to 1000-fold improvement in detection limit was observed. The application of an inductively coupled plasma optical emission spectrometry (ICP-OES) instrument (a PerkinElmer Optima 4300DV) with flow injection hydride generation (FI-HG) sample handling (a PerkinElmer FIAS 400) as a method for the determination of selenium was described. The flow injection signals were processed by version 3.0 of PerkinElmer's Winlab32 ICP software that allows time-based transient signals to be processed, as well as the normal wavelength-based transients obtained with steady-state sample introduction. The FI-HG-ICP-OES was coupled to online preconcentration. A silica-based Discovery SAX resin was used as a preconcentration material for selenite. The method was used to determine percent recovery of low ppt levels of Se in different water samples such as spring water, river water, lake water, and seawater. The use of the Multi Mode Sample Introduction System (MSIS™) was also evaluated for the determination of selenium. The efficiency of the HG procedure improved the detection limit by 100 fold when compared to that of conventional nebulization. The procedure also allowed better tolerance to interfering ions. The Se uptake of Brassica napus was investigated. Different Se species were added to the soil and hydroponic media. Selenomethionine and the "newly identified selenoaminoacid", S-(methylseleno)cysteine were identified in the plant extracts by gas chromatography with atomic emission detection (GC-AED). Ion exchange chromatography with inductively coupled plasma mass spectrometry detection (IC-ICP-MS) was developed to identify the Se species in total parenteral nutrition (TPN) and the urine of neonates. Since the identity and amount of the selenium used in supplementation is known, identifying the resulting metabolites can give a new aspect on the selenium metabolic pathway in neonates. Preliminary determination of selenite by GC-AED was investigated. Inorganic Se in the form of selenite (SeO32-) was converted to piazselenol. The use of both 2,3-diaminonaphthalene and 4-chloro- o-phenylendiamine as derivatizing agents was investigated.

Determination of hydride -forming elements by atomic spectrometry

Rodriguez Toledo, Yustina 01 January 2006 (has links)
The parameters affecting the generation of stibine (SbH3) from homogeneous borohydride solutions and immobilized borohydride were evaluated for a flow injection system coupled to a quartz tube atomic absorption spectrometer. The stibine release and transport efficiency were affected by the design of the hydride generator and the vapor generation conditions. A new method for the determination of antimony by quartz tube atomic absorption spectrometry with flow injection chemical vapor generation from a tetrahydroborate-form anion exchanger was developed. Flow injection hydride generation parameters were optimized. Several samples could be injected before the column was reloaded with borohydride. Interferences from transition and hydride forming elements and signal suppression due to high ionic strengths were eliminated. The developed method was successfully applied for the determination of antimony in spiked natural waters. Several synthetic organic cation exchangers, inorganic ion exchangers and organic sorbent ion exchangers were evaluated as selective sorbents for inorganic antimony preconcentration without prior complexation. Neither the organic cation exchangers, nor the organic sorbent ion exchangers gave good results. Only one of the inorganic ion exchangers evaluated gave satisfactory results. The different parameters affecting the generation of arsine, bismuthine and hydrogen selenide from immobilized borohydride were evaluated by using a flow injection system coupled with a quartz tube atomic absorption spectrometer. Hydrides from these elements were generated from immobilized borohydride in the presence of other hydride-forming elements. In all cases, multiple injections were made before the column needed to be reloaded with borohydride. A new method for the simultaneous determination of antimony, arsenic, bismuth, selenium, tin and mercury by flow injection chemical vapor generation atomic emission spectrometry with tetrahydroborate immobilized on a strong anion exchange resin was developed for the first time. Both flow injection and vapor generation parameters were optimized. Simultaneous vapor generation, good sensitivities and low detection limits were achieved. The developed method was successfully applied to the determination of antimony, arsenic, bismuth, selenium, tin and mercury in natural water samples and a standard reference material with satisfactory results. Preliminary results for chemical vapor generation of manganese, zinc, nickel, cobalt, iron and lead were obtained.


COLELLA, MICHAEL B 01 January 1980 (has links)
Abstract not available


KOSTYLA, ROBERT JOSEPH 01 January 1980 (has links)
Abstract not available


WALTERS, FREDERICK HENRY 01 January 1976 (has links)
Abstract not available


LONGMOORE, KENNETH JOSEPH 01 January 1981 (has links)
Part I: Indirect determination of trace Organic Functional Groups Via Atomic Absorption Spectroscopy. Three indirect analysis techniques for the determination of isothiocyanates, dialkyl disulfides, and carbonyls have been developed. The isothiocyanate functional group is determined by conversion of the isothiocyanate to the substituted thiourea in an ammoniacal solution. The thiourea is desulfurized with a silver amine reagent, producing a silver sulfide precipitate. The precipitate is isolated by filtration, digested in acid, and diluted in an aqueous solution. The silver content is determined by Atomic Absorption Spectroscopy (AAS). The technique has a 0.5 - 20.0 micromole working range with a 2-4% relative standard deviation. The dialkyl disulfide is determined by reduction of the disulfide in ammoniacal sodium sulfite at 50(DEGREES). The resultant mercaptide is precipitated as the silver salt, isolated by filtration, dissolved, and determined by AAS. The technique has a 1.0 - 10.0 micromole working range with a 4-8% relative standard deviation. The carbonyl functional group was determined by treating the carboxyl with hydroxylamine hydrochloride to form the oxime product and acid. A measured quantity of ammonia was added as a proton scavenger to force the reaction to completion. The excess ammonia was determined by adding a nickel dimethyl glyoxime solution to both the sample and blank. The change in nickel concentration (from the isolated precipitate) is proportional to the carbonyl content. The nickel was determined by AAS. The technique has a working range of 1.0 - 10.0 micromoles with a 4-8% relative standard deviation. Part II: Immobilized Functional Groups For The Selective Concentration Of Trace Organics. Three different types of functional groups have been immobilized on insoluble supports for the purpose of selectively concentrating trace organics from aqueous and non-aqueous media via functional group reactions. A bis-dianilino ethane functional group was immobilized on a polyacrylate support which was selective for aldehydes in the presence of ketones. The capacity of the resin for various aldehydes was examined. The condensation product, a tetrahydroimidazole, may be acid hydrolyzed to the diamine and the original aldehyde compound. This reaction is employed to recover the sequestered compound. Several hydrazine related functional groups were examined to evaluate their utility as immobilized functional groups for carbonyl concentrating procedures. Four functional groups were evaluated. Carbazide, semithiocarbazide, acid hydrazide, and hydrazine resins were prepared. The semithiocarbazide resin was found to be the most efficient for carbonyl uptake. An isothiuronium salt was immobilized on a polystyrene backbone for the selective reaction with carboxylic acids. The resin was evaluated on the basis of batch equilibration studies, reaction kinetic studies, and column concentration/recovery studies. Solutions of 80 ppb of carboxylic acids were quantitatively recovered with a 100 fold concentration. The intent of this work was to develop novel functional group analysis techniques which may be employed at trace level concentrations.

The oxygen inductively coupled plasma discharge for spectrochemical analysis

Yang, Pengyuan 01 January 1987 (has links)
An low-power oxygen ICP discharge has been investigated theoretically and experimentally. Temperature and flow fields have been calculated by computer simulations. The electron temperature and density, intensity ratio of ion line to atom line, and excitation temperature have been measured and compared with the LTE values. The analytical features also are evaluated. The low-power oxygen ICP discharge has been converted from a pre-running argon plasma. The torch used in the normal argon plasma is applied without modifications. The whole procedure is simplified to two steps, with a total conversion time of 1 minute. A new computer simulation method developed for an industrial plasma has been modified and applied to the analytical plasma. The two-dimensional electromagnetic field and the swirl force effect have been included in the computation. The oxygen plasma operated at the high frequency and low power now can be simulated at various operating conditions. The electron temperature for the low-power oxygen plasma has been measured and are in good agreement with the one predicted by the computer simulation. The excitation temperature has been calculated from the measurement of Boltzmann distribution of Fe I population levels and are found to be close to the electron temperature. The distribution of electron number density has been measured from the H alpha line width. The experimental results for the ratio of intensities of Ca II to Ca I and of Cd II to Cd I are in good agreement with the ones predicted by a LTE model, which confirms the oxygen plasma is close to LTE. In addition to LTE properties, the charge transfer from oxygen ions has been confirmed as an important excitation mechanism process. The detection limits for thirty eight elements have been measured and are generally 10 times poorer than in an argon plasma, but are still better than in an air or nitrogen plasma. BaO powder sample has been analyzed. A more than 10 times improvement has been observed for the signal to background ratio of Ba II line when compared to those in argon plasma.


COURNOYER, ROBERT FREDERICK 01 January 1974 (has links)
Abstract not available

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