Browsing by Subject "Gas chromatography."
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Item Design and synthesis of novel β-cyclodextrins and their application as chiral stationary phases for gas chromatography.(2011-01-05T19:46:00Z) Hayden, Tiffany Renee Turner.; Garner, Charles M. (Charles Manley), 1957-; Chemistry and Biochemistry.; Baylor University. Dept. of Chemistry and Biochemistry.Enantiomers can be directly separated only with use of systems containing a chiral selector. Cyclodextrins (CDs) and modified cyclodextrins have been used as chiral selectors for their ability to form host-guest complexes with various analytes. The scaffold of the CD allows for assembly of functional groups with controlled geometry. CDs can be readily modified through substitution of the hydroxyl groups, giving rise to derivatives with significantly different properties, especially increased solubility and controlling the hydrophobicity of the cavity. Even though CDs can be readily modified, the syntheses can be tedious and complicated with various protecting group strategies to control the reactivity of the various alcohols. The preparation of modified cyclodextrins for use as chiral stationary phases (CSP) for gas chromatography (GC) is the focal point of this research. Our effort to identify useful new β-CD derivatives involved attempts to make bridged (annulated) derivatives, could increase the thermal stability of the derivatives, and change the length, width and polarity of the CD cavity. To date, there are no reports of annulated CD derivatives in the chemical literature. In the process of evaluating a wide range of electrophiles that could accomplish annulation, several new β-CD derivatives, i.e., per(6-O-TBS-2,3-O-cyclodimethylsilyl)- β-CD, per(6-O-TBS-2,3-O-cyclodiphenylsilyl)- β-CD, per(6-O-Pivaloyl-2,3-O-cyclodimethylsilyl)-β-CD, per(6-deoxy-2,3-O-methyl)- β-CD, and per(6-deoxy-2,3-O-allyl)- β-CD, were synthesized. Two of the new derivatives were evaluated as components of stationary phases for GC, per(6-O-TBS-2,3-Ocyclodimethylsilyl)-β-CD and per(6-deoxy-2,3-O-methyl)-β-CD. Overall, this work resulted in five new CD derivatives.Item Determination of pharmaceuticals and personal care products in fish using high performance liquid chromatography-tandem mass spectrometry and gas chromatography-mass spectrometry.(Washington, DC : American Chemical Society Publications., 2007) Ramirez, Alejandro Javier.; Chambliss, C. Kevin.; Brooks, Bryan W.; Chemistry and Biochemistry.; Baylor University. Dept. of Chemistry and Biochemistry.Labeled as emerging organic contaminants, pharmaceuticals and personal care products (PPCPs) have been the focus of global environmental research for over a decade. PPCPs have caused widespread concern due to their extensive use. As PPCPs were designed to correct, enhance, or protect a specific physiological or endocrine condition, their target effects in humans and/or farm stocks are relatively well understood and documented. However, there is limited knowledge about their unintended effects in the environment. To address the occurrence, distribution and fate of PPCPs in the environment, efficient and reliable analytical methods are needed. The relatively low concentration, high polarity, and thermal lability of some PPCPs, together with their interaction with complex environmental matrices, makes their analysis challenging. Sample preparation followed by GC or HPLC separation and mass spectrometry (MS) detection has become the standard approach for evaluating PPCPs in environmental samples. PPCPs have been widely reported in water, sediment and biosolids, but reports of their occurrence in aquatic organisms have been limited by the difficulty of analysis. Herein, we report the first HPLC-MS/MS screening method for the analysis of 23 pharmaceuticals and 2 metabolites representing multiple therapeutic classes in fish tissues. The developed methodology was successfully applied to assess the occurrence of target analytes in fish collected from 8 locations throughout the United States (6 effluent-dominated rivers and two reference sites). A complementary GC-MS method was developed for the analysis of 12 additional compounds belonging to either personal care product or industrial use compound classes in fish muscle. This approach was also applied to screen for target analytes in fish collected from a regional effluent-dominated stream.Item The preparation of novel modified cyclodextrins and their application in enantioseparations by gas chromatography.(2010-06-23T12:27:03Z) Allen, Sheree N.; Garner, Charles M. (Charles Manley), 1957-; Chemistry and Biochemistry.; Baylor University. Dept. of Chemistry and Biochemistry.Since biological processes depend on the stereospecific creation and conversion of chiral molecules, each enantiomer of a molecule can have a different biological effect. While numerous synthetic drugs are sold in racemic form for reasons of cost and convenience, in many cases one of the two enantiomers of a drug will cause undesirable and perhaps even devastating effects. Therefore, effective methods for the separation and quantification of enantiomers are of great importance. Enantiomers can be separated only with the use of systems containing an optically active chiral selector. Modified cyclodextrins (CDs) are widely used as chiral selectors by virtue of their ability to form inclusion complexes. Because of the remarkably high efficiency, and sensitivity of chiral gas chromatography (GC), chiral separations by this method represent a preferred method for enantiomer analysis. The basic property of CDs that allows them to be successful for enantiomer separations is their ability to form selective inclusion complexes with a wide variety of organic molecules. The preparation and application of modified cyclodextrins for the GC separation of enantiomers is a focal point of this research. In effort to identify useful new derivatives, modifications involving unique and separate reaction of the secondary hydroxyl groups and/or annulations bridging the secondary oxygens have been examined. Several new cyclodextrin derivatives, e.g. per(6-OTBS-2,3-O-diformyl)-β-CD, per(6-OTBS-2,3-O-cyclodimethylsilyl)-β-CD, per(6-deoxy-2,3-O-cyclodimethylsilyl)-β-CD and a mixed formyl/acetyl phase have been synthesized and evaluated as components of stationary phases for capillary GC. The efficiency of each new phase to separate enantiomers was evaluated against a 30 analyte panel to evaluate the influence of the different substituents on the selectivity. These enantioseparations were also compared to those observed on four commercially available chiral phases using the same 30 analyte panel. Overall, this work resulted in nine new CD derivatives and the discovery of a new chiral selector that is comparable in efficiency to what is currently commercially available.