Thesis (PhD)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: Even capillary gas chromatography does not always give complete separation of the components of complex mixtures. During the last few decades several two-dimensional gas chromatographic techniques were developed to circumvent this problem and towards the end of the previous century, a technique that became known as comprehensive twodimensional gas chromatography, was introduced with which the peak capacity of capillary gas chromatography could be increased by at least two orders of magnitude. This technique is based on utilizing different separation mechanisms of two coupled chromatographic columns to get a better separation of complex mixtures than would be possible with the individual columns. To be classified as comprehensive twodimensional gas chromatography, the analytes eluted from the first or primary column must al be transferred to the second column as sharp sample pulses by, for example, focusing of analytes. Focusing of the analytes can be achieved by trapping or immobilizing the analytes in a short capillary tube that serves as a connection between the two columns, after which the trapped material is released as a sharp pulse into the secondary column by rapidly, i.e. within a fraction of a second, heating this capillary which therefore serves to modulate the effluent from the primary column. This ensures optimum separation on the secondary column and the independence of retention times of the analytes on the two columns. A modulator consisting of a capillary (modulator capillary) coated with a thick film of an apolar stationary phase was used in the present project to immobilize or trap the analytes. This capillary was housed in a stainless-steel tube (heater) which was subdivided into a number of segments of equal lengths (maximum of 10). These segments were heated sequentially to desorb the analytes from the inlet end of the modulator to its outlet end at such a rate as to generate and transfer a sharply focused analyte pulse into the secondary column. In a typical analysis each of the 10 segments of a lO-segment heater would, for example, be heated to a temperature 50°C higher than that of the gas chromatograph's oven (50°C temperature increment) within 200 milliseconds, after which each segment would be allowed to immediately cool down to the temperature of the oven. After the last segment had been heated, a pause of, for example, two seconds followed to allow analytes to be trapped in the modulator capillary after which the cycle was repeated until the analysis had been completed. For several reasons, heating the segments resistively by using a current of between 1 and 20 Ampere was preferred to the application of high voltages. A computer controlled power supply was developed with which any combination of duration of the energizing pulses of the segments from 10 to 2500 milliseconds, pause times from 100 milliseconds to 100 seconds and temperature increments of 100°C or higher could be used with acceptable precision and high reproducibility in comprehensive two-dimensional gas chromatographic analyses. The effectivity of the focusing that can be achieved with heaters having different numbers of segments, modulator capillaries with different inside diameters, different heating increments, as well as different rates at which the modulators are heated, were investigated. The best results were obtained with heaters having 8 and 10 segments, a modulator capillary with an inside diameter of 0.2 mm, a heating increment between 50°C and 10Goe, and a heating cycle composed of a total heating time of two seconds followed by a pause time of two to three seconds before the next cycle is started. A light petroleum oil fraction was used in a preliminary evaluation of the comprehensive two-dimensional system that was developed. At this stage of the project the influence of various parameters such as the average carrier gas velocity, the temperature program and the length of the secondary column was investigated. It was found that changing one parameter required the re-optimization of the other parameters. The concentrations of the sample also had a marked influence on the parameters that had to be used to achieve optimum results. A low sample concentration appeared to require a higher carrier gas velocity, a higher temperature-programming rate or considerably longer pause times to achieve satisfactory focusing of analytes, whereas too high a concentration resulted in breakthrough of the analytes from the modulator capillary. The two-dimensional gas chromatographic device was also interfaced to a quadrupole mass spectrometer. A GC-MS analysis of a petroleum oil sample gave mass spectra of surprisingly good quality in spite of the high scanning speed that was required by the sharp constituent peaks produced by the gas chromatographic component of the system. The two-dimensional system that was developed therefore appears to offer a costeffective alternative to other systems that have been developed elsewhere in which other modulation mechanisms are used. One remaining problem that still has to be solved is the unsatisfactory synchronization of the timing device of the power supply with that of the computer on which data are accumulated. Although the difference in timing may seem negligible, the result is that certain software packages cannot be used for the two-dimensional visualization of the data Of several possible solutions to the problem, redesigning the control circuitry of the power supply will be the first option to be explored. An important consideration in the development of the system was to avoid having moving parts so that the modulator could be installed in any gas chromatograph without requiring structural alterations to the instrument. No provision was therefore made to install the two columns and the modulator in separate temperature-programmable compartments in the oven of the gas chromatograph. During the evaluation of the present system it was, however, found that the parameters which gave acceptable results were confined to rather narrow limits. Not being able to cool the modulator to temperatures below that of the oven was found to be the most important limiting factor. A simple solution to this problem is to cool the modulator to a selected suitable temperature below the oven temperature with compressed air, the flow of which is regulated by a computer controlled mass flow regulator to maintain the same increment below the oven temperature right through an analysis. As this development was considered to be outside the scope of the present project, this idea was not implemented and evaluated. However, successful exploratory experiments were done in which the flow was mechanically regulated. A prototype of the component in which the modulator can be cooled was built and the mass flow regulator, control unit and software will be commissioned shortly. / AFRIKAANSE OPSOMMING: Volledige skeiding van die verbindings in 'n komplekse mengsel is selfs met kapillêre gaschromatografie nie altyd moontlik nie. Oor die afgelope paar dekades is verskillende tweedimensionele gaschromatografiese tegnieke ontwikkel om hierdie probleem te bowe te kom en redelik onlangs is 'n tegniek bekend gestel wat as omvattende tweedimensionele gaschromatografie bekend staan en wat die piekkapasiteit van 'n kapillêre gaschromatografiese skeiding teoreties met sowat twee ordegroottes kan verhoog. Hierdie tegniek berus op die aanwending van die verskillende skeidingsmeganismes van twee chromatografiese kolomme wat aan mekaar gekoppel word en waardeur verbeterde skeiding van komplekse mengsels verkry kan word. Hierdie tegniek kan egter slegs as omvattende tweedimensionele gaschromatografie beskou word as die analiete wat van die primêre kolom elueer volledig na die sekondêre kolom oorgedra word in die vorm van skerp gedefinieerde monsterpulse, byvoorbeeld deur fokussering van analiete. Fokussering van die analiete kan verkry word deur die eluaat van die primêre kolom te immobiliseer in 'n kort kapillêr tussen die twee kolomme waarna dit as 'n skerp puls op die sekondêre kolom ingelaat kan word deur die kapillêr, wat dus as modulator dien, vinnig, dit wil sê binne breuke van 'n sekonde, te verhit. Hierdeur word optimum skeiding in die sekondêre kolom verseker asook die onafhanklikheid van die retensietye van verbindings op die twee kolomme. In hierdie projek is gebruik gemaak van 'n modulator wat bestaan uit 'n kapillêr (modulatorkapillêr) belaag met 'n dik laag van 'n apolêre stasionêre fase om die analiete te immobiliseer. Die kapillêr is in 'n vlekvrye staalbuis (verhitter) geplaas wat in 'n aantal gelyke segmente verdeel is (maksimum van 10) en die segmente is vinnig opeenvolgend verhit om die analiete vanaf die inlaat- na die uitlaatkant van die modulator uit die stasionêre fase in die kapillêr te desorbeer en as 'n skerp gefokusseerde puls na die sekondêre kolom oor te dra In 'n tipiese analise sou elkeen van die segmente van 'n 10- segment verhitter, byvoorbeeld, binne 200 millisekondes tot 'n temperatuur 500e hoër as die temperatuur van die gaschromatograafoond (500e verhittingsinkrement) verhit word, waarna die betrokke segment toegelaat word om oombliklik tot die oondtemperatuur af te koel. Na verhitting van die laaste segment volg 'n wagtyd van, byvoorbeeld, twee sekondes om analiete wat uit die primêre kolom elueer toe te laat om in die modulatorkapillêr gesorbeer te word waarna die siklus herhaal word tot die einde van die analise. Om verskeie redes is besluit om die segmente elektries te verhit deur verkieslik hoë stroomsterktes van tussen 1 en 20 Ampere te gebruik in plaas daarvan om van hoë spannings gebruik te maak. 'n Gerekenariseerde kragbron is ontwikkel wat dit moontlik gemaak het om enige kombinasie van verhittingstyd per segment tussen 10 en 2500 millisekondes, wagtye van 100 millisekondes tot 100 sekondes tussen verhittings en temperatuurinkremente van 100°C en selfs hoër met bevredigende presisie en hoë reproduseerbaarheid vir omvattende tweedimensionele gaschromatografiese skeidings te gebruik. Ondersoek is ingestel na die effektiwiteit van fokussering wat verkry word deur verhitters met verskillende getalle segmente, modulatorkapillêre met verskillende binnedeursnitte, verskillende verhittingsinkremente, asook verskillende tempo's waarteen die modulatorkapillêr verhit word, te gebruik. Die beste resultate is verkry met 8- en 10- segment verhitters, 'n modulatorkapillêr met 0.2 mm binnedeursnit, 'n verhittingsinkrement tussen 50°C en 100°C en 'n verhittingsiklus bestaande uit 'n twee sekonde totale verhittingstyd gevolg deur twee tot drie sekondes wagtyd voor die volgende siklus begin. 'n Ligte aardolie-fraksie is gekies as die eerste monster vir die evaluering van die omvattende tweedimensionele sisteem wat ontwikkel is. In hierdie stadium van die projek is die invloed van verskillende parameters soos die gemiddelde vloeisnelheid van die draergas, die temperatuurprogram, asook die lengte van die sekondêre kolom ondersoek. Daar is gevind dat verandering van een parameter, byvoorbeeld die lengte van die sekondêre kolom, die heroptimering van die ander parameters vereis. Die konsentrasie van die monster het ook 'n bepalende invloed op die parameters wat 'n optimum skeiding van verbindings lewer. 'n Lae konsentrasie mag 'n hoër vloei, vinniger temperatuurprogram of heelwat langer wagtyd vereis om bevredigende fokussering van die analiete te verkry, terwyl 'n te hoë konsentrasie tot deurbraak van die analiete in die modulatorkapillêr kan lei. Die tweedimensionele gaschromatografiese sisteem IS ook aan 'n kwadrupoolmassaspektrometer gekoppel en analise van 'n aardolie-monster het massaspektra van verbasende goeie kwaliteit gelewer ten spyte van die hoë skandeerspoed wat deur die baie smal gaschromatografiese pieke wat deur die sisteem geproduseer word, vereis word. Die tweedimensionele sisteem wat ontwikkel is, stel klaarblyklik 'n kosteeffektiewe alternatief daar vir die enkele ander sisteme wat deur ander navorsingsgroepe ontwikkel is en waarin van ander modulatortipes gebruik gemaak word. Een oorblywende probleem is egter die onbevredigende sinchronisasie van die tydhousisteme van die kragbron en die rekenaar waarmee die data versamel word. Hoewel uiters gering, bring die verskil in tydsmeting van die twee komponente mee dat sekere sagtewarepakette nie vir die tweedimensionele voorstelling van die data gebruik kan word nie. Vanverskillende moontlike oplossings vir hierdie probleem, sal die herontwerp van die beheerstelsel van die kragbron eerste ondersoek word. 'n Belangrike oorweging ill die ontwikkeling van die huidige sisteem was om 'n modulator sonder bewegende dele te ontwikkel wat sonder moeite in enige gaschromatograaf geïnstalleer sou kon word. Daar is dus nie voorsiening gemaak vir die installering van die twee kapillêre kolomme en die modulator in afsonderlik temperatuurprogrammeerbare kompartemente in die gaschromatograafoond rue. Gedurende die ondersoek het dit egter geblyk dat die parameters wat bevredigende resultate lewer, as gevolg van hierdie ontwerpskriterium, tussen redelike nou grense lê. Die mees beperkende faktor is die feit dat die modulator nie benede die oondtemperatuur afgekoel kan word nie. 'n Eenvoudige oplossing vir hierdie probleem is afkoeling van dié modulator tot 'n geskikte selekteerbare temperatuur benede dié van die gaschromatograafoond met druklug waarvan die vloei met behulp van 'n rekenaarbeheerde klep geprogrammeer kan word. Aangesien hierdie ontwikkeling buite die bestek van die huidige ondersoek geval het, is die idee nie geïmplementeer en volledig geëvalueer nie. Voorlopige eksperimente waarin die lugvloei meganies beheer is, is wel suksesvol uitgevoer. 'n Prototipe van 'n geskikte onderdeel waarin die modulator afgekoel word, is vervaardig en die massavloeiregulerende klep, beheereenheid en sagteware sal eersdaags in gebruik geneem word.

No description available.

The aim of this investigation was to develop and test a theory that allowed for the calculation of the activity coefficients at infinite dilutions (l' ~ 3) from G.L.C. measurements using moderately volatile solvents. The solvents chosen for study were straight chained (Cs to C7) and cyclic (Cs, C6 and benzene) liquid hydrocarbons using cis- and trans-decahydronaphthalene (decalin) as the stationary liquid phase (solvent). The systems were studied at two different temperatures, 283.15 K and 298.15 K. The solutes were n-pentane~ n-hexane, n-heptane, cyclopentane, cyclohexane and benzene. This method for the determination of activity coefficients has the advantage of being able to work at infinite dilution, whereas in other techniques, extrapolation to infinite dilution of finite-concentration data is necessary. In addition solutes are separated from impurities when chromatographed so that only very small quantities of moderately pure material need be· used. However the technique is also limited since the solute studied (injected reagent) needs to be volatile, while the solvent (liquid stationary phase) should be involatile. The solvents chosen in this experiment (cis- and transdecalin) are moderately volatile which introduces many limitations since the theory developed for the determination of activity coefficients at infinite dilution is restricted to involatile solvents. However a novel method for working with moderately volatile solvents is developed by relating the loss of solvent to its partial pressure and modifying the existing theory. In the past the use of precolumns and/or saturators, coarse packing, small pressure gradients, and internal standards were used when working with volatile solvents. However employing this new method excludes the use of precolumns, saturators, or internal standards, and allows any type of packing and pressure gradient to be used. The calculated activity coefficients are compared with literature values, where the wor~ers employed G.L.C. techniques, and with predicted values. The activity coefficients calculated at both temperatures are used in the calculation of excess partial molar enthalpies. These results are compared with values obtained from finite concentration data by other workers. / Thesis (M.Sc.)-University of Natal, Durban, 1992.

Yeung Wing Cheung. / Bibliography : leaf 91 / Thesis (M.Phil.)--Chinese University of Hong Kong, 1982

by Lung Man Tung. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1991. / Includes bibliographical references. / ACKNOWLEDGMENT --- p.i / ABSTRACT --- p.ii / Chapter CHAPTER 1 --- GENERAL INTRODUCTION --- p.1 / Chapter 1.1 --- Stationary phases and detectors --- p.2 / Chapter 1.2 --- Internal standardization --- p.5 / Chapter 1.3 --- Common pre-treatment technique --- p.6 / Chapter 1.4 --- Pre-treatment techniques --- p.9 / Chapter 1.5 --- Objectives of this work for the determination of styrene --- p.11 / Chapter CHAPTER 2 --- EXPERIMENTAL --- p.13 / Chapter 2.1 --- Instrumentation --- p.13 / Chapter 2.2 --- Reagents and solutions --- p.16 / Chapter 2.3 --- Preparation of stock solutions --- p.18 / Chapter 2.4 --- Sample preparation --- p.19 / Chapter 2.5 --- Extraction method for food samples --- p.20 / Chapter 2.6 --- Procedure for the analytical finish --- p.22 / Chapter 2.7 --- Assessment of the food matrix effect on the recovery of styrene --- p.23 / Chapter 2.8 --- Confirmatory Procedures --- p.23 / Chapter 2.9 --- Treatment of data --- p.24 / Chapter CHAPTER 3 --- DEVELOPMENT OF METHOD --- p.26 / Chapter 3.1 --- Development of GC method --- p.26 / Chapter 3.2 --- Development of the extraction method --- p.29 / Chapter CHAPTER 4 --- DETERMINATION OF RESIDUAL STYRENE IN POLYSTYRENE POLYMER --- p.50 / Chapter 4.1 --- The proposed method --- p.50 / Chapter 4.2 --- Identification of polymer and one cup for the ice-cream cone --- p.51 / Chapter 4.3 --- Determination of residual styrene monomer in polystyrene container and cup --- p.52 / Chapter CHAPTER 5 --- DETERMINATION OF STYRENE MONOMER MIGRATED INTO FOODSTUFFS --- p.58 / Chapter 5.1 --- Methodolgy and scope --- p.58 / Chapter 5.2 --- Determination of styrene migrated into ice-cream --- p.59 / Chapter 5.3 --- Determination of styrene migrated into Yakult and Yogo --- p.60 / Chapter 5.4 --- Determination of styrene migrated into foodstuff kept at elevated temperature in polystyrene containers --- p.60 / Chapter 5.5 --- Conclusion --- p.74 / REFERENCES --- p.76 / APPENDIX --- p.80

Pharmaceuticals are a group of emerging organic compounds of environmental concern used extensively in human and veterinary medicine. They are continually released into the environment as a result of manufacturing operations and excretion from humans and animals. These compounds enter directly into the municipal sewage systems and into wastewater treatment plants. A large number of important and potentially harmful organic contaminants, such as these pharmaceuticals, are not regulated in drinking and other waters. As a result, conventional technologies at most waste water treatment plants (WWTPs) discharge water that meet regulatory standards, yet are not specifically designed to remove these organic contaminants. Therefore, pharmaceutical compounds and their metabolites remain in discharged effluent and enter into the natural aquatic environment. Concentrations of pharmaceutical residues measured in water are typically reported in the ranges of ug/L to ng/L, which are at least three to four orders of magnitude lower than that required to produce a pharmacological effect. The probability of risks to humans arising from such an acute exposure is unlikely, but the possible effects resulting from life-long exposures and synergistic effects from exposure to many chemicals have yet to be determined. It has been widely reported that pharmaceuticals and their metabolites that enter into the aquatic environment can have a potential harmful effect on the aquatic ecosystem and can reach drinking water sources. This research focuses on non-steroid anti-inflammatory drugs (NSAIDs), a group of pharmaceuticals which are widely used as analgesic, antipyretic and anti-inflammatory agents. NSAIDs are frequently used because they are easily accessible as over the counter medication and are a group of drugs that do not produce addiction, respiratory depression, or drowsiness. There is an incentive for removing NSAIDs and other pharmaceuticals from the aquatic environment. Thus, quantitative evaluation of the fate of pharmaceuticals, proper risk assessment and improvement of the efficiency of WWTPs need sensitive and reliable analytical methods. The purpose of this project was to provide a method for detecting three common NSAIDs, IBF, KTF, and NAP, in purified water with LLE-GC-FID. And, an investigation of UV photolysis, UV/H2O2, and UV/TiO2 AOPs was performed to determine their effectiveness in treating IBF, KTF, and NAP in purified water. All treatment methods were successful in degrading target compounds with a total degradation of 86% or greater after 45 minutes. A liquid-liquid extraction technique using methylene chloride and BSTFA + 1%TMCS derivatizing agent was determined for detecting low concentrations of IBF, KTF, and NAP with calibration curves showing good linearity with all R2 values greater than 0.9880.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 1979. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Vita. / Includes bibliographical references. / by John Milan Lavoie, Jr. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Vita. / Includes bibliographical references. / by Agnes Van Langenhove. / Ph.D.

No description available.

An oscillating plasma glow discharge detector for gas chromatography is used to obtain fingerprint information about an analyte by combining both the average cell current and oscillation frequency signals. Five homologs each of the n-alkanes, 1-alkenes, 1-alkynes, 2-ketones and aldehydes are studied. Although triplicate determinations had some scatter due to noise, they showed clustering that allows several of these compounds to be distinguished from the others by using a two-dimensional plot of the ratios of frequency peak area to current peak area and frequency peak height to current peak height. Fingerprint identification information is improved by changing the cell pressure, applied voltage and electrode spacing. Changes in the discharge operating conditions produce changes in the analyte peak responses. The relative magnitudes of the analyte current and frequency peak responses also change with respect to each other under different discharge conditions. Unique fingerprints or patterns of responses are created for each analyte by changing the discharge operating conditions. The detector responses toward 10 organic compounds, representing seven different functional groups, are recorded under 56 different combinations of discharge conditions. The ratios of the frequency to current peak responses (heights and areas) for three of the 56 sets of conditions investigated provide enough information to distinguish between nine compounds. Principal component analysis and hierarchical cluster analysis, multivariate exploratory techniques, are used to observe natural clustering in the data. / Graduation date: 1994