Academic literature on the topic 'Chromatorgraphy'

The paper studied the thermal mechanical shearing of waste tire rubber (WTR) by tetra methyl thiuram disulfide (TMTD), a reclaiming agent. The results showed that the mooney viscosity, gel content and crosslink density of the WTR decreased with the increasing TMTD amount. The mechanical properties of recycled rubber were best in the amount of 1% TMTD, which could reach 14MPa and 368%, respectively. The molecular weight of WTR was analyzed by gel permeation chromatorgraphy (GPC). The molecular weight of rubber dropped more faster when the content of TMTD from 0.5% to 1%. The plausible reaction mechanism of TMTD on the process of cross-linking degradation was predicted based on the changes of the mooney viscosity, gel content, crosslink density and the relation between the molecular weight and the Raman spectroscopy of the sol fraction.

Water soluble compounds were extracted from the dominant cryptogams of the Windmill Islands, Wilkes Land, and compared with standard polyols, sugars and amino acids using 13C nuclear magnetic resonance (NMR) spectroscopy. Previous findings for sugars and polyols from gas liquid chromatorgraphy were validated and extended. Arabitol, ribitol and mannitol were confirmed as the major soluble carbohydrate compounds in all lichen species examined. Sucrose, fructose and glucose, but no polyols were detected in two species of moss. Sorbitol was confirmed as a major component of the algae Prasiola crispa and Schizogonium murale. Mesotaenium bergrenii was confirmed to contain sucrose and glucose. No significant quantities of sugars or polyols or any other compound were found in extracts of the red snow alga Chloromonas sp.1. Amino acids were detected in the majority of cryptogam samples and were particularly abundant in the algae P. crispa and S. murale. In the latter species the total identified acids ranged from 13.5–66mg g-1 dry weight. In addition to the common amino acid components of proteins, betaine and γ-amino-butyric acid were detected, the latter being particularly abundant, being found widely in the moss, lichen and algae. Several unknown carbohydrates were characterized. Usnea sphacelata, U. antarctica and Pseudephebe minuscula contained a deoxy-hexitol, Grimmia antarctici contained resonance peaks consistent with a trisaccharide containing a sucrose moiety and Umbilicaria decussata possibly contained a glucose-arabitol dimer. 13C NMR was confirmed as a powerful tool for the characterization of low molecular weight constituents of Antarctic cryptogams.

A reversed phase-high performance liquid chromatography method has been developed that is capable of resolving lead and cadmium diethyldithiocarbamate complexes. The method does not require the presence of hazardous solvents to optimize peak shape and resolution; the mobile phase consists of methanol, water, and a surfactant. Tobacco samples were chemically oxidized and reacted with sodium diethyldithiocarbamate reagent prior to analysis using the HPLC method. The lead diethyldithiocarbamate determination was compromised by the presence of a significant interference in the analysis; lead determinations in 10 foreign and domestic tobacco samples ranged from 27.14 to 134.84 μg/g. The cadmium diethyldithiocarbamate determination was not adversely affected by interferences. Cadmium determinations in 10 foreign and domestic tobacco samples ranged from 0.89 to 6.96 μg/g. The tobacco samples were also analyzed using atomic absorption spectrometry. Foreign tobacco brands that contained clove as a spice showed lower levels of cadmium and lead.

Thesis (MSc)--Stellenbosch University, 2011.
ENGLISH ABSTRACT: This study focused on the potential of comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC×GC-TOF-MS) for the improved analysis of volatile wine constituents. Solid phase microextraction (SPME) in combination with GC×GC-TOF-MS was successfully used for the detailed investigation of the impact of three commercial Oenococcus oeni lactic acid bacteria (LAB) strains on the volatile composition of Pinotage wines subjected to malolactic fermentation (MLF). Due to increased separation power and enhanced sensitivity obtained by using two orthogonal separations coupled with the structural information provided by deconvoluted TOF-MS spectra, GC×GC-TOF-MS allowed for the identification and semi-quantitative analysis of much larger numbers of compounds compared to previous studies applying one-dimensional gas chromatography. The combination of univariate and multivariate statistical assessment was used as a powerful tool for data interpretation. The obtained results contribute significantly to the understanding of the impact of MLF on the volatile composition of Pinotage wine Some compounds have been linked to MLF for the first time. Moreover, the impact of these commercial starter cultures on the composition of volatile sulfur and nitrogen compounds in the same wines was studied by one-dimensional gas chromatographic methods with headspace injection and solid supported liquid-liquid extraction together with sulfur selective detection and tandem mass spectrometry. This study demonstrated also for the time, the impact of MLF on the composition of volatile sulfur and nitrogen compounds in Pinotage wine. GC×GC-TOF-MS was further used for the evaluation of the suitability of a new phase for stir bar sorptive extraction (SBSE) analysis of wine volatiles. Despite instrumental complications, beneficial extraction properties of the new stir bar phase for especially more polar compounds could be demonstrated. In addition, the extraction ability of this novel phase was evaluated for the analysis of selected thiazoles in wine using heart-cutting two dimensional gas chromatography in combination with nitrogen selective detection. Advantageous extraction performance of the new stir bar phase compared to a conventional polydimethylsiloxane (PDMS) phase for the determined thiazoles was demonstrated.
AFRIKAANSE OPSOMMING: Hierdie studie het gefokus daarop om die potensiaal van omvattende tweedimensionele gaschromatografie gekombineer met vlugtyd massaspektrometrie (GC×GC-TOF-MS) vir die verbeterde analise van vlugtige wynkomponente te ondersoek. Soliede fase mikro-ekstraksie (SPME) in kombinasie met GC×GC TOF MS is met sukses aangewend vir ‘n ondersoek na die impak van drie kommersiële Oenococcus oeni melksuur bakteria (LAB) rasse op die samestelling van die vlugtige fraksie van Pinotage wyne wat appelmelksuurgisting (AMG) ondergaan het. As gevolg van die verbeterde skeidingsvermoë en die verhoogte sensitiwiteit wat verkry word deur twee ortogonale skeidings te kombineer, tesame met die inligting aangaande die molekulêre struktuur wat die die gedekonvoleerde TOF massaspektra verskaf, maak GC×GC-TOF-MS die identifikasie en semi-kwantitatiewe analise van aansienlik meer komponente, in vergelyking met die gebruik van een-dimensionele gaschromatografie, moontlik. Die kombinasie van monoveranderlike asook multiveranderlike statistiese evaluering is gebruik as ‘n kragtige tegniek vir data interpretasie. Die resultate wat verkry is dra tot ‘n groot mate by tot die ontrafeling en begrip aangaande die impak wat AMG op die samestelling van vlugtige komponente in Pinotage wyn het. Daar word ook vir die eerste keer aangetoon dat somminge komponente verband te hou met AMG. Aanvullend hiertoe is die impak wat hierdie kommersiële kulture (wat gebruik word om fermentasie te inisieer) op die voorkoms van swawel en stikstof bevattende vlugtige komponente het bestudeer deur gebruik te maak van een-dimensionele gaschromatografiese metodes met ‘headspace’ inspuiting en vloeistof-voeistof ekstraksie tesame met swawel en stikstof selektiewe deteksie en tandem massaspektrometrie. Hierdie ondersoek werp lig, ook vir die eerste keer, op die samestelling van vlugtige swawel en stikstof bevattende komponente in Pinotage wyn. GC×GC-TOF-MS is ook gebruik vir die evalueering van die toepaslikheid van ‘n nuwe stasionêre fase vir gebruik met roerstaaf sorptiewe ekstraksie (SBSE) vir die analisering van vlugtige komponente in wyn. Ten spyte van instrumentele komplikasies, is die voordele wat hierdie nuwe fase vir die ekstraksie van vernaamlik meer polêre komponete aangetoon. Vervolgens is die ekstraksievermoë van hierdie nuwe fase vir die analise van sekere tiasole in wyn met ‘heart-cutting’ twedimensionaly gaschromatografie in kombinasie met stikstof-selektiewe deteksie gedemonstreer. Verbeterde ekstraksie van die nuwe roerstaaf fase vir die analise van tiasole, in vergelyking met ‘n tradisionele polydimethylsiloxane (PDMS) fase is voorts aangetoon.

Les lipoprotéines de haute densité (High Density Lipoprotein, HDL) permet deréduction de risque de maladies cardio-vasculaires principalement en raison de leurcapacité à éliminer le cholestérol accumulé des artères (via transport inverse ducholestérol). Les effets protecteurs des HDL sont médiés par l'apolipoprotéine AI(ApoA1), qui est le La protéine la plus importante quantitativement du HDL. L’ApoA1favorise l'efflux de cholestérol vers le foie pour l'excrétion. Une augmentation desniveaux plasmatiques de l’ApoA1 est généralement acceptée d'êtrecardioprotecteur, ce qui en fait un potentiel thérapeutique. Deux variantes naturelle(mutants) de l’ApoA1, Milano et Paris, sont caractérisées par une mutationponctuelle unique a permis l'introduction d'un résidu cystéine. Populations avecApoA1-Milano ont été rapportés d'avoir un système cardiovasculaire, même avec defaibles niveaux de plasma de ApoA1 et HDL. Il est donc d'intérêt pour générerrecombinante de type sauvage et des variantes de ApoA1 humaine pour desapplications thérapeutiques potentielles. Dans cette étude, de type sauvagerhApoA1 a été produit chez P. pastoris et purifié par chromatographie en modemixte en une seule étape. Par la suite, un processus intégré a été le développementde la production et la récupération rapide de type sauvage rhApoA1 chez P. pastorispar chromatographie par lit expansée. En outre, les variantes de l'ApoA1, Milano &Paris, ont été générées par mutagenèse dirigée et ont été exprimés chez P. pastoris.Les motifs d’adsorption de rhApoA1-Milano et rhApoA1-Paris ont été comparés àcelle de type sauvage ApoA1 et les différences ont été discutées
The high-density lipoprotein (HDL) complex helps reduce the risk of cardiovasculardisorders mainly due to its ability to remove accumulated cholesterol from arteriesvia reverse cholesterol transport. These protective effects of HDL are known to bemediated by Apolipoprotein A-I (ApoA1), which is the major protein component ofHDL. ApoA1 is a lipid binding protein and promotes cholesterol efflux fromperipheral tissues to the liver for excretion. An increase in the plasma levels ofApoA1 is generally accepted to be cardioprotective, making it a potentialtherapeutic. Two naturally occuring variants of ApoA1, namely the Milano & Parismutants, are characterised by a single point mutation resulting in the introduction ofa Cysteine residue. Populations with ApoA1-Milano have been reported to have ahealthier cardiovascular system even with low plasma levels of ApoA1/HDL. It ishence of interest to generate recombinant wild type and variants of human ApoA1for potential therapeutic applications. In this study, wild type rhApoA1 was producedin P. pastoris and purified by mixed-mode chromatgraphy in a single step.Subsequently, an integrated process has been development for the production andrapid recovery of wild type rhApoA1 in Pichia pastoris. This has paved way to theestablishment of a scalable integrated process that could be further developed toindustrial levels. In addition, the cysteine variants of ApoA1, Milano & Paris, havebeen generated by site directed mutagenesis and have been successfully expressedin P. pastoris. The binding patterns of rhApoA1-Milano and rhApoA1-Paris have beencompared with that of wild-type ApoA1 and the differences have been discussed