Selenium has been shown to have multiple biochemical effects ranging from nutrient deficiency at low levels to toxicity at high levels. This duality of concern has led to a demand for increased numbers of highly accurate and precise determinations of selenium in biological materials. A convenient procedure was developed for determining selenoamino acids by HPLC-THG-AAS, based on the derivatization of these analytes with Sanger's reagent. Selenomethionine, selenocystine and selenocysteine (after blocking the free selenol group with phenylmercurio cation) were converted to their N-2,4-dinitrophenyl derivatives, and separated on a Nucleosil 5-NO$ sb2$ column with methanolic mobile phase containing acetic acid and triethylamine. Furthermore, an improved HPLC-AAS interface design was modified and optimized for the detection of selenium in HPLC column eluate. The new design was (i) compatible with aqueous mobile phases containing volatile buffers and (ii) provided equivalent molar response to analytes containing Se($-$II), Se(+IV) and Se(+VI). A method for simultaneously determination of selenate, selenite, selenocystine, selenomethionine and selenoethionine was developed by using the HPLC-AAS system with aqueous acetic acid containing ammonium acetate as eluate solution on the cyanopropyl column. The equivalent low ng limits of detection (1-2 ng as Se) for different oxidation states of selenium analytes were obtained using several different mobile phases and/or columns. A phenol extraction procedure for selenate, selenite, selenocystine, selenomethionine and selenoethionine was evaluated for the determination of these selenium analytes in natural waters and wheat samples. The current HPLC-AAS system provides an inexpensive alternative to conventional techniques for the determination of selenium analytes in environmental samples.

Standards of Amadori rearrangement products (ARP) were synthesized for the purpose of developing analytical techniques and performing mechanistic studies related to their thermal decomposition. Several synthetic strategies were explored. An HPLC analytical system with a diode array detector was coupled to a fluorometer and an electrochemical detector, in order to detect simultaneously and on-line, a wide variety of degradation products of ARPs and to follow their kinetics. The potential of such a system to analyze complex Maillard mixtures was demonstrated. The kinetics of the reaction of glucose with morpholine (a Strecker inactive analogue of proline was used in order to simplify the kinetics) to produce Amadori morpholine was studied under experimental conditions that minimize side reactions and maximize Amadori product formation. At specific time intervals, the samples were analyzed for the presence of reactants and Amadori product by the multidetector HPLC system. Color and fluorescence were also measured. The data obtained were used to calculate the rate constants for the formation and degradation of Amadori product. A mechanistic model that statistically fitted the kinetic data was proposed. To further understand the details of the decomposition mechanism of Amadori proline, different mass spectrometric experiment were performed. High resolution, linked-field scan and neutral loss experiments have indicated that 1-((2$ sp prime$-carboxyl)pyrrolidinyl)-1-deoxy- scD-fructose (Proline Amadori product) followed two main pathways of fragmentation under electron impact conditions; one initiated by the ring oxygen and the other by the amino acid nitrogen, producing two well stabilized fragment ions; oxonium and imminium ions. In addition, ortho-elimination reactions initiated by O or N-centered radical sites were shown to produce the most intense peaks and diagnostically important ions for the identification of Amadori products. However this approach can only pro

The need for selective and inexpensive detectors in liquid chromatography is of considerable interest in the determination of sulfur compounds. Of the available-selective sulfur methodologies, flame photometric detector coupled to gas chromatography is the most widely used. It has proven to be a sensitive and selective method for detection of heat stable and volatile sulfur compounds. Fundamentally, this technique is not applicable to high boiling and/or thermolabile sulfur compounds. More recently, hyphenated flame photometric detector has been utilized, with limited success, to monitor sulfur species in liquid chromatography. However, existing HPLC-FPD methodologies have never been applied to real samples, due to the low population of S 2, the emitting species, and the quenching effects of the other species present in the flame. / In this work, two total consumption high-performance liquid chromatography flame photometric (HPLC-FPD) interfaces compatible with either methanolic or aqueous mobile phases are described and optimized for monitoring low volatile and thermally fragile sulfur compounds in biological samples. Each interface was fuelled either by methanol or by hydrogen. The all quartz interfaces enclosed four consecutive thermal processes: (a) thermovaporization of the HPLC effluent; (b) pyrolysis of the organic matrix (including sulfur species) in a kinetic H2/O2 flame; (c) conversion of the oxidized sulfur compounds to H2S in a reducing post-combustion stage fuelled by hydrogen; and (d) transport of the generated hydrides towards a hydrogen radical rich surrounding of an inverted hydrogen-oxygen diffusion flame. Chemiluminescence induced in the last step was integrated as a narrow beam in a light-guide positioned remotely from the analytical cool flame and oriented towards a photomultiplier unit. Radioisotopic assays demonstrated that sulfur (as H235SO4) was transferred quantitatively to the analytical flame. Indirect evidence suggested that sulfur was hydrogenated in the post-combustion step via a thermochemical hydride generation process to mediate the formation of S2. The linearity of calibration graphs (0.9950 < r < 0.9986), where r is the correlation coefficient) and unprecedented HPLC-FPD limits of detection for sulfur compounds (1.5 etag/s for 2-methylthiophene, 2.25 etag/s for carbon disulfide, and 4.5 etag/s for ethanesulfonic acid) allowed for the speciation of sulfur species in garlic extracts. Alternatively, modification of the methanol fuelled interface to a hydrogen fuelled reactor allowed detection of thiosulfinates and high molecular weight sulfur compounds in horse kidney and garlic extracts, respectively.

The design and construction of an electrochemical detector with two working electrodes located on the opposite walls of a thin-layer cell and its use as a detector for High Pressure Liquid Chromatography (HPLC) in the analysis of catecholamines in human cerebrospinal fluid are described. The location of the electrodes in this manner permits an electrochemically reversible or quasireversible couple to be electrolized more than once as it passes through the detector. If one electrode is held at a potential where oxidation takes place and the second electrode at a potential where reduction of this oxidized form back to the starting material occurs, then the current produced increases proportionately to the number of conversions that take place. A comparison of this cell in the dual-working-electrode and single-working-electrode mode shows an improvement in the signal-to-noise ratio by a factor of six. This HPLC system with electrochemical detection has been used for the first time to detect norephinephrine (141 pg/mL) and dopamine (262 pg/mL) in human cerebrospinal fluid.

No description available.

Graduation date: 1992

Graduation date: 1994

For pain research, the orofacial region is unique in a number of ways. The region has complex local anatomy, including substantial sensory innervation from neural pathways, and muscles of facial expression that convey important information concerning pain intensity and associated psychological traits. Although chronic orofacial pain conditions appear prevalent, useful documentation on pain intensity ratings using well established instruments is sparse. In particular, two conditions, atypical facial pain and atypical odontalgia, are poorly understood in aetiology so that definitive treatment modalities are severely limited. The region's local biofluid, saliva, has been used to diagnose various local and systemic disease states, and to quantitate drug concentrations. However, recent studies indicate that saliva also contains some of the same peptides, e.g. bradykinin, that are involved in pain mechanisms. It may be that pharmacological-pharmacokinetic studies of these peptides could shed more information on thesignificance of their presence in saliva. This thesis consists of four major sections. Section 1 comprises of three clinical studies investigating orofacial pain. Section 2 deals with clinical laboratory studies of saliva. Section 3 is concerned with the development of chromatographic methods to assay bradykinin and its pharmacokinetics in saliva. Section 4 uses chromatography for the identification of novel salivary peptides. This thesis, then, presents clinical studies of orofacial pain and pharmacological investigations of saliva as the local biofluid.

Thesis (PhD (Paraclinical Sciences))--University of Pretoria, 2006. / Includes bibliographical references.

Thesis (Ph.D.)--Case Western Reserve University, 2009 / Department of Biomedical Engineering Abstract Title from OhioLINK (viewed on 20 April 2009) Available online via the OhioLINK ETD Center