Orientador: Rubens Maciel Filho / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica / Made available in DSpace on 2018-08-01T13:16:30Z (GMT). No. of bitstreams: 1 Santos_MarcelaG.Motados_M.pdf: 3608818 bytes, checksum: dd58239af4dfd4bf4e0e40b36a9134e5 (MD5) Previous issue date: 2000 / Resumo: Desde a terceira década do século XX, tem-se realizado o processo de extração de oleaginosas utilizando como solvente o hexano. Como esta substância é tóxica e altamente inflamável, tem-se intensificado a procura por solventes que produzam óleo de boa qualidade utilizando tecnologias limpas minimizando o prejuízo ao meio ambiente e também ao ambiente de produção. É neste contexto que está sendo estudada a substituição do hexano por solventes supercríticos, que são não só solventes efetivos para a extração, mas também apresentam uma série de peculiaridades que os tornam mais vantajosos em relação aos solventes líquidos, geralmente usados. Além das características inerentes aos meios supercríticos, o dióxido de carbono tem-se tornado um solvente potencial para a substituição do hexano por ser não tóxico, não inflamável, por apresentar condições supercríticas relativamente brandas (temperatura crítica de 31°C e pressão crítica de 73.8 bar), além de estar disponível a baixo custo. O objetivo deste trabalho é estudar o comportamento de uma planta de extração supercrítica. Além disso será realizada a análise de sensibilidade paramétrica para a avaliação do comportamento de determinadas variáveis na performance do processo, baseada nos conceitos do planejamento fatorial. Neste trabalho é apresentado um modelo que usa parâmetros experimentais para avaliar políticas de controle e otimização. Partindo deste modelo foi realizada a análise de sensibilidade paramétrica, que possibilitou estudar tanto os efeitos principais das perturbações nas variáveis como os efeitos de interação destas variáveis. A partir disso foi possível determinar as variáveis de maior influência no processo, e, desta forma, determinar estratégias de otimização do processo. Além disso foi avaliada também a estabilidade da solução numérica do modelo apresentado para o método de solução utilizado / Abstract: Since the third decade of the century XX, it has been accomplishing the extraction process of oleaginous for hexane. As this substance is toxic and highly flammable, it has been intensifying the search of solvents that produce oil of good quality using clean technologies, minimizing the damage to the environment and production envirenment. It is in this context that is being studied the substitution of the hexane by supercritical solvents, which are not just effective solvents for the extraction of oil of seeds, but they also present a series of peculiarities they turn them more advantageous in relation to the liquid solvents, generally used. Besides the inherent characteristics to the supercritical means, the carbon dioxide has been proving a potential solvent for the substitution of the hexane for being not toxic, not flammable, to present supercritical conditions relatively mild (critica I temperature of 31°C and critica I pressure of 73.8 bar), besides being at a low cost available.The objective of this work is to study the behavior of a supercritical extraction plant. Besides the parametric sensibility analysis is accomplished for the evaluation of the behavior of certain variables in the precess performance, based on the concepts of the factorial designo. In this work a model is presented that uses experimental parameters for evaluations of control politics and optimization. Starting from this model took place the parametric sensitivity analysis, which facilitated to study the principal and interaction effects of perturbations in certain variables. Starting frem that it was possible to determine the variables of larger influence in the process, and, this way, to determine strategies of the process optimization. Besides the stability of the numeric solution of the model for the used solution method was also evaluated. / Mestrado / Desenvolvimento de Processos Químicos / Mestre em Engenharia Química

Orientadores: Maria Angela de Almeida Meireles, Paulo de Tarso Vieira e Rosa / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-04T11:45:06Z (GMT). No. of bitstreams: 1 QuispeCondori_Socrates_D.pdf: 2798950 bytes, checksum: 0b1d9044fdb82444a8064327ee12685a (MD5) Previous issue date: 2005 / Resumo: No presente trabalho é apresentado um estudo global do processo de extração de produtos naturais usando dióxido de carbono supercrítico como solvente. As duas etapas do processo foram estudadas usando diversas matrizes vegetais. Na Etapa de Extração (Artemisia annua, Cordia verbenacea e Ocimum selloi) foram medidos dados de rendimento global para os três sistemas. Para os sistemas CO2 + A. annua e CO2 + C. verbenacea foram calculados os parâmetros cinéticos do processo de extração e um modelo matemático foi selecionado para representar as curvas globais de extração. A técnica de extração fracionada foi aplicada para os sistemas CO2 + C. verbenacea e CO2 + Ocimum Selloi. A determinação do rendimento global permitiu visualizar o efeito da temperatura e pressão sobre a solubilidade do extrato, além de proporcionar informações necessárias para modelagem do processo de extração. A condição que maximizou o rendimento em extrato nos sistemas CO2 + A. annua e CO2 + C. verbenacea foi 300 bar / 50 °C. Entretanto, foi demonstrado que o extrato de C. verbenacea obtido nesta condição apresenta menor atividade anticâncer àquele obtido a 200 bar / 40 °C. Para o sistema CO2 + Ocimum Selloi o maior rendimento foi obtido a 200 bar / 40 °C. No estudo da cinética do processo de extração foi verificado que para o sistema CO2 + A. annua a vazão do solvente foi o único fator significante sobre os parâmetros cinéticos. No estudo do efeito da altura do leito para o sistema CO2 + C. verbenacea, verificou-se que os parâmetros cinéticos aumentam com a altura do leito. Na modelagem matemática das curvas globais de extração (OEC) dos sistemas CO2 + A. annua e CO2 + C. verbenacea verificou-se que os modelos de Naik et al. [1989] (empírico), Sovová [1994] e Goto et al. [1993] apresentaram os melhores ajustes aos dados experimentais. Do estudo do efeito da altura do leito na SFE a partir de C. verbenacea, verificou-se que a seleção de um modelo para aumento de escala é difícil de ser realizada, uma vez que o modelo selecionado nem sempre é válido para todos os ensaios. Na Etapa de Separação (Foeniculum vulgare) foi realizado o estudo da influência das condições operacionais (temperatura, pressão e vazão do solvente) na recuperação do extrato. As condições de temperatura e pressão de separação foram determinadas através de modelagem termodinâmica usando-se a equação de estado de Peng-Robinson. A determinação do comportamento da solubilidade dos componentes majoritários do extrato de F. vulgare (anetol e ácido oléico) em CO2 supercrítico permitiu obter uma aproximação das condições ótimas de separação. No estudo da influência das condições operacionais (temperatura e pressão) determinou-se que o aumento da pressão no primeiro separador permite a solubilização do compostos de maior massa molecular, os quais são transferidos para o segundo separador. Entretanto, se o objetivo for o fracionamento do extrato de F. vulgare, observou-se que a melhor condição operacional para separação da fração rica em componentes de óleo volátil foi 80 bar / 40 °C no primeiro separador. Foi verificado também que o aumento da vazão de solvente diminui o rendimento em anetol e funchona e, conseqüentemente, no rendimento global. A otimização das condições de separação da mistura extrato + solvente é uma etapa importante do processo de extração de produtos naturais usando fluidos supercríticos, uma vez que permitirá uma ótima recuperação e/ou fracionamento do extrato / Abstract: In the present work a global study of the extraction of natural products using supercritical carbon dioxide as solvent is presented. The two steps of the SFE process were studied using several raw materials. In the Extraction Step (Artemisia annua, Cordia verbenacea and Ocimum selloi), global yield data for the three plants were determined. Kinetic parameters of the extraction process were calculated for the CO2 + A. annua and CO2 + C. verbenacea systems and a mathematical model to represent the overall extraction curves was selected. The fractional extraction technique was applied for the CO2 + C. verbenacea and CO2 + Ocimum Selloi systems. The determination of the global yield allowed to identify the effect of the temperature and pressure on the solubility of the extract, besides providing necessary information for the modeling of the extraction process. The operational condition that maximized the global yield in the systems CO2 + A. annua and CO2 + C. verbenacea was 300 bar / 50 °C. However, it was demonstrated that the C. verbenacea extract obtained at this condition shows a lower anticancer activity than that obtained at 200 bar / 40 °C. The higher global yield for the CO2 + Ocimum Selloi system was obtained at 200 bar / 40 °C. In the study of the kinetic of the extraction process for the CO2 + A. annua system, it was verified that the flow rate was the only significant factor on the kinetic parameters. In the study of the effect of the extraction bed height for the CO2 + C. verbenacea system, it was verified that the kinetic parameters increase with the bed height. The Naik et al. [1989] (empirical), Sovová [1994] and Goto et al. [1993] models presented the best fittings to the experimental overall extraction curves (OEC) for the CO2 + A. annua and CO2 + C. verbenacea systems. From the study of the effect of the height of the bed for the C. verbenacea, it was verified that the selection of a mathematical model to scale-up is difficult to be accomplished, because the selected model is not always valid for all experiments. In the Separation Step (Foeniculum vulgare) the study of the influence of the operational conditions (temperature, pressure and flow rate) in the recovery of the extract was carried out. The temperature and pressure of the separation step was calculated through thermodynamic modeling using the equation of state of Peng-Robinson. The determination of the solubility behavior of anethole and oleic acid (major compounds of the F. vulgare extract) with supercritical CO2 allowed to obtain an approximation of the optimal condition of the separation step. In the study of the influence of temperature and pressure, it was determined that the increase of pressure in the first separator allows the solubilization of high molecular mass compounds that are transferred to the second separator. However, if the objective is the fractionation of the fennel extract, it was observed that the best operational condition to separate a rich fraction in volatile oil compounds was 80 bar / 40°C. Additionally, it was verified that the increase of flow rate diminishes the anethole and fenchone yields and, consequently, the global yield. The optimization of the operational conditions in the separation of the mixture extract + solvent is an important step in the supercritical extraction of natural products, because it will allow an optimal recovery and/or fractionation of the extract / Doutorado / Engenharia de Alimentos / Doutor em Engenharia de Alimentos

Master of Science / Food Science Institute / Jayendra K. Amamcharla / In recent years, the interest in functional components such as phospholipids (PLs) is increasing as a result of growing awareness of their health benefits. PLs affect several cell functions, such as growth, molecular transport system, memory processing, stress responses, and central nervous system myelination. Many studies have shown that the neutral lipids can be successfully extracted using supercritical carbon dioxide (SCO₂) from different types of foods such as egg, canola, pumpkin seed, fish and dairy powders. It is an alternative method to avoid the use of large quantities organic solvents. The SCO₂ is a safe, environmentally friendly and economical process to extract edible lipids from a variety of matrices. However, a modifier such as ethanol is needed to fractionate PLs due to limited solubility of PLs in SCO₂. The objectives of this study were to optimize the SFE process parameters and to determine the effect of pressure, temperature, and ethanol concentration on the extraction efficiency of PLs from whey protein phospholipid concentrate (WPPC) and buttermilk powder (BMP). Three different batches of WPPC and BMP were obtained from a commercial manufacturer and followed a unique two-step extraction process to isolate PLs from WPPC and BMP. In Step-1, neat supercritical CO₂ was used to remove all the neutral lipids at 414 bar pressure, 60 °C sample temperature, and 5 L/min CO₂ flow rate. The spent solids, the powder left after the first step extraction, were used to extract PLs in the second step. The Step-2 (SCO₂-Ethanol) process was optimized in terms of pressure (350, 414 and 550 bar), temperature (40 °C and 60 °C) and concentration of ethanol (10%, 15% and 20%) as independent factors. All the lipid fractions were analyzed by high performance lipid chromatography (HPLC) and thin layer chromatography (TLC). For WPPC, only ethanol concentration had significant effect (P < 0.05) on the amount of PLs extracted after the Step-2. On the other hand, temperature and ethanol concentration were significantly (P < 0.05) affected the efficiency of SFE for BMP. The optimal processing conditions for WPPC and BMP were 350 bar pressure, 60 °C sample temperature and 15% concentration of ethanol, and 550 bar of pressure, 60 °C sample temperature and 15% concentration of ethanol, respectively. This study allowed obtaining PLs from dairy co-products such as WPPC and BMP as a separate ingredient and this could be useful in nutraceutical and infant formulations as well as different food products formulations.

Orientadores: Osvaldir Pereira Taranto, Theo Guenter Kieckbusch / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-18T13:08:50Z (GMT). No. of bitstreams: 1 Paes_MarianaSchincariol_M.pdf: 5069814 bytes, checksum: a63adbbd40bd6a5a6b57af8796d19087 (MD5) Previous issue date: 2011 / Resumo: Óleo essencial é uma mistura de componentes voláteis produzido por vegetais e tem as funções de proteção contra predadores e de atrair agentes polinizadores. É utilizado pelas indústrias de alimentos, de cosméticos e também pela farmacêutica. O rendimento e a composição do óleo essencial variam de acordo com inúmeros fatores, dentre eles as condições de acondicionamento da matéria-prima e de extração empregados. O presente trabalho teve como objetivo estudar a influência do tratamento precedente à extração de óleo essencial de rizomas e de tubérculos moídos de Cyperus articulatus L., conhecido como priprioca, no rendimento e na composição do produto. Para isso foram empregados a secagem natural e os secadores do tipo leito fluidizado pulsado e estufa, operados em três diferentes níveis de temperatura (40, 50 e 60°C). O óleo essencial foi extraído com CO2 supercrítico de matéria-prima com três diferentes faixas de diâmetro (0,15-0,30; 0,42-0,575 e 0,70-0,85mm). Foi observado que não há diferenças estatísticas entre os rendimentos de óleos essenciais obtidos através do emprego de diferentes secadores operados sob a mesma condição de temperatura. Os resultados de rendimentos foram favorecidos quando usadas partículas com menores faixas de diâmetro em todas as condições de secagem empregadas. O uso de maiores temperaturas de secagem reduziu significativamente o rendimento somente quando utilizado o secador leito fluidizado pulsado. As análises cromatográficas dos óleos essenciais e também o uso de detector de massas permitiram identificar como principais componentes os sesquiterpenos mustakona e corimbolona. A presença dos monoterpenos foi favorecida quando utilizadas temperaturas amenas de secagem e, em algumas situações, o uso de partículas com maiores diâmetros também favoreceu a obtenção dos monoterpenos / Abstract: Essential oil is a mixture of volatile components produced by plants whose functions are protecting against predators and attracting pollinator agents. Essential oils are used by the food, cosmestic and farmaceutical industries. The yield and composition varies according to many factors, such as the raw-material storage conditions and the extraction process adopted. This work aimed to study the influence of the treatment of ground tubercles and rhizomes of Cyperus articulatus L., known as "priprioca", on the essential oil yield and composition. Therefore, the raw material was submitted to three different drying methods prior to the extraction process: a natural drying, a pulsed fluidized bed dryer and oven. The dryers were used in three different temperature levels (40, 50 and 60°C). The essential oil was extracted with supercritical CO2 from priprioca particulate in three different diameter ranges. The results demonstrated no difference between the essential oil yield obtained by different dryers at the same temperature condition. Whereas, the yield was improved by the usage of smaller particles in all drying conditions. Higher temperatures in the pulsed fluidized bed reduced significantly the essential oil yield. The sesquiterpenes mustakone and corymbolone were observed by gas chromatography analysis with mass detector as the two major components. The monoterpenes presence was improved when mild drying conditions were used and, in some cases, the usage of larger particulates also improved monoterpenes attainment / Mestrado / Engenharia de Processos / Mestre em Engenharia Química

Orientador: Maria Angela de Almeida Meireles / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-26T21:20:51Z (GMT). No. of bitstreams: 1 Jesus_SusanaPereirade_D.pdf: 19153904 bytes, checksum: e8d3e5239f2dbe5f9d61e1e553bad266 (MD5) Previous issue date: 2015 / Resumo: A extração supercrítica consiste em uma operação unitária de separação na qual o solvente é um fluido no estado supercrítico, sendo que o dióxido de carbono (CO2) é o mais utilizado. Destaca-se por ser reconhecida como uma tecnologia limpa, alternativa aos métodos convencionais que em geral utilizam solventes orgânicos prejudiciais à saúde e ao meio-ambiente. O processo de extração supercrítica tem sido extensivamente estudado pela comunidade científica há mais de três décadas, o que resultou na construção de um sólido conhecimento sobre os principais fundamentos envolvidos neste processo, além da formação de uma ampla base de dados para descrever o comportamento de diferentes sistemas (CO2 + matriz sólida). É uma técnica de extração a alta pressão que começou a ser utilizada em escala comercial na década de 1980 e, desde então, o número de plantas em operação é crescente em algumas regiões como Europa, Ásia e Estados Unidos. Apesar disso, continua a ser considerada uma tecnologia emergente e inovadora, visto que os métodos convencionais ainda são predominantes em diversas aplicações industriais e, em muitos países (como é o caso do Brasil), a técnica ainda não é utilizada em escala comercial. A viabilidade técnica do processo de extração supercrítica já está consolidada e a tecnologia encontra-se disponível comercialmente. Além disso, pesquisadores da área afirmam que a técnica pode ser economicamente competitiva, dependendo da área de aplicação e do produto de interesse. Entretanto, a questão econômica ainda é considerada como o principal empecilho à disseminação desta técnica, pois os custos de investimento associados a uma planta de alta pressão são altos quando comparados à instalação de plantas que operam em baixas pressões. Diante deste cenário, considera-se importante a investigação de métodos de cálculo (modelagem e simulação) que possam ser aplicados no sentido de estimar parâmetros para design de processo e aumento de escala, os quais são requeridos em estudos de viabilidade econômica. No presente trabalho, dados disponíveis na literatura foram utilizados para estudar a modelagem matemática da transferência de massa no processo de extração supercrítica. Para tanto, dados cinéticos de matérias-primas diversas foram ajustados por meio da aplicação de diferentes modelos, tendo como foco avaliar a versatilidade e aplicabilidade dos mesmos em termos de design de processo. Os resultados demonstraram que o modelo spline e o modelo de Sovová foram eficientes na descrição quantitativa da curva de extração, além de apresentarem versatilidade para ajustar curvas com formatos diferenciados. O modelo spline apresentou os melhores ajustes e também menores erros na descrição da etapa CER (Constant Extraction Rate), a qual é a mais importante em termos de design de processo / Abstract: Supercritical fluid extraction (SFE) is a solid-fluid separation technique in which the solvent is a fluid in the supercritical state, and the supercritical carbon dioxide (CO2) is the most used one. It is recognized as a green technology and a versatile alternative to conventional extraction methods, which generally use organic solvents that are harmful to human health and environment. The SFE process has been extensively studied by scientific community for more than three decades. As a consequence, a solid knowledge about the fundamental concepts has been developed, and there is a huge amount of data to describe the behavior of different systems (CO2 + solid matrix). It is a high-pressure extraction method that has been carried out on a commercial scale since the 1980s. From that point on, a growing number of industrial plants have been operating in Europe, Asia, and USA. However, SFE can still be considered an emerging technology since the conventional methods remain the most used in various applications. Besides, this technique has yet not been applied on a commercial scale in several countries, such as Brazil. The technical feasibility of SFE process is consolidated and the industrial-scale technology is commercially available. Researchers in this field claim that costs of SFE may be commercially competitive, depending on application area and target products. Nonetheless, the economic aspects are still considered an obstacle in SFE technology dissemination. This happens especially because a high pressure process requires higher investment costs than a conventional low pressure plant. In this scenario, it is important to investigate calculation methods (modeling and simulation) that may be applied to estimate parameters for process design and scale-up, which are key points in studies of economic viability. In this work, the mathematical modeling of SFE mass transfer was investigated by using experimental data from literature. Then, different models were applied to fit the kinetic data of SFE from various raw materials. The main purpose was to evaluate the models by considering their versatility and applicability in terms of process design. The results showed that spline and Sovová¿s models have been very effective in describing the quantitative behavior of the extraction curves. Moreover, these models presented versatility in fitting different curve shapes. The spline model provided the best fits as well as the lowest residual errors in the CER (Constant Extraction Rate) period, which is the most important region for process design purposes / Doutorado / Engenharia de Alimentos / Doutora em Engenharia de Alimentos

No description available.

Supercritical fluid extraction (SFE) is an alternative to traditional extractions with organic solvents. SFE consists of removing the analyte(s) from the matrix, solubilizing them, moving the analyte(s) into the bulk fluid, and sweeping the fluid containing the analyte(s) out of the extraction vessel. As the fluid leaves the extraction vessel, decompression of the fluid occurs, changing its volume and temperature which can lead to analyte loss. This work focussed on the trapping process with the restrictor immersed in a liquid after SFE. Experiments compared the effects of trapping parameters on the collection efficiencies of fat-soluble vitamins of similar polarities and structures. The most important variable was the selection of collection solvent and its physical properties, such as viscosity, surface tension and density were found to be important. Additionally, adding a modifier to the collection solvent in an attempt to change its physical properties and influence collection efficiencies for a polarity test mix was studied. Addition of a modifier can improve collection efficiencies and allow higher collection temperature to be used, but the modifier did not increase trapping recoveries to the extent that collection pressurization did. The occurrence of a methylation reaction of decanoic acid during the SFE and collection processes, using a methanol modified fluid or collection solvent was investigated. The majority of the reaction occurred during the collection process and the degree of methylation was found to be dependent on temperature, but not on static or dynamic extraction time. When no additional acidic catalyst other than carbon dioxide in the presence of water was present, conversion was limited to about 2%, but was quantitative with an added acidic catalyst. The last portion of this work involved the application of the SFE process to the extraction and analysis of extractable material in eight hardwood and softwood pulp samples. Grinding the samples increased extractable fatty acid methyl esters (FAMEs) by ten-fold, and in-situ derivatizations resulted in higher FAME recoveries than derivatization after SFE. Liquid trapping enhanced recoveries of lower FAMEs when compared to tandem (solid/liquid) trapping. In-situ acetylations sometimes yielded acetylated glucoses. Large differences in FAMEs concentrations were seen for hardwood samples, but lesser differences were seen for the softwood pulp samples. / Ph. D.

This work examines the use of supercritical fluid extraction (SFE)as a sample introduction technique for supercritical fluid chromatography (SFC) and Fourier transform infrared spectrometry (FT-IR). In order to study the effects of a supercritical mobile phase on the resulting IR spectra, carbon dioxide was compared to xenon as a supercritical fluid mobile phase for flow cell SFC/FT-IR. A packed capillary column (30 cm x 320 μm, Deltabond® Cyano, 5 μm particle) was employed for the chromatographic portion of the study. Various samples were tested, such as an ethoxylated alcohol mixture and a unique polarity mix. The roles of temperature and density on the IR spectra were also examined as each was independently varied for the analysis of five different probe compounds. Comparisons of spectra produced in supercritical CO₂ and xenon each matched well with the Nicolet vapor phase library. CO₂ spectra matched the vapor phase spectra equally as well as did the xenon spectra, despite the fact that CO₂ spectra have blanked regions where the mobile phase absorbs in the IR. Following this study, SFE was coupled directly to FT-IR to produce the novel method of on-line SFE/FT-IR. This technique was optimized for the analysis of n-tetracosane, yielding a detection limit of 74 ng. The method was later applied to the quantitative and qualitative analysis of fiber finishes from textile matrices with equivalent success. Finish was extracted directly from the fiber or textile surface and passed through the IR flow cell as an analyte "plug". In this way, the entire finish was quickly quantified, and if desired, qualitatively analyzed as well, without need of prior chromatographic separation. The method required no organic solvent and was proven to be fairly reproducible for four fiber finish types tested. Lastly, supercritica1 fluid extraction (SFE) was examined and optimized as a sample introduction technique for on-line SFE/SFC. Trapping and recovery of analytes in SFE/SFC were studied under varying conditions using a currently marketed system. The system was replumbed using a 12 cm x 100 μm fused silica capillary (100% methyl, d_f = 0.25 μm) for trapping and increased solute focusing. These changes nearly doubled the total analyte recovery (as based on FID peak areas) and lowered the overall system recovery RSDs from 30 % to 4 %. / Ph. D.

A method has been developed for the quantitative extraction of nitrotoluenes (2,6-dinitrotoluene, 2,4-dinitrotoluene, and trinitrotoluene) from water. Three types of solid sorbents were investigated: two 47 mm Empore disks™ - octadecylsilane (C18) and styrene-divinylbenzene (SDVB); and one Bakerbond spe*™ Phenyl stationary phase. The phenyl sorbent yielded the highest recoveries. The average SPE recoveries for spike standards ranged from 80 to 95 percent for Millipore water and 55 to 95 percent from well and surface water in the low ppb and ppt levels. After the nitrotoluenes were trapped on the solid sorbents they were quantitatively eluted by first doping the bed with toluene and then extracting with supercritical carbon dioxide. Doping with toluene was found to increase the rate of extraction. The extracts were analyzed off-line via GC-ECD using an internal standard. Extraction losses are due to analyte break through, and not from poor SFE recoveries. This demonstrates that supercritical fluid extraction is a suitable elution technique for analytes trapped on solid phase extraction (SPE) cartridges. A method has also been developed and evaluated for the direct on-line coupling of SPE to GC. SPE-SFE-GC-ECD analysis eliminates off-line collection and subsequent handling of hazardous materials. SFE is an ideal means of directly coupling SPE to GC, since carbon dioxide is a gas at ambient temperatures and pressures and thus easily removed. One potential problem for SPE-SFE on-line GC is the presence of residual water trapped on the active sites of the bonded silica sorbent. The presence of water can interfere with the cryogenic trapping of the analytes on the capillary GC column. The water becomes ice at cryogenic temperatures and in large quantities blocks the GC column. This problem has been avoided by using a split injection interface previously described by Hawthorne. The quantitative reproducibility of this interface will be investigated for nanogram quantities of nitroaromatics. / Ph. D.

The introduction of supercritical CO₂ at packed column supercritical fluid chromatography (SFC) flow rates is shown to significantly affect the excitation characteristics of a helium microwave induced plasma (He MIP). In this work, the influence of CO₂ on specific atomic and ionic transitions of Cl, Br, I, P, and S is described. Also presented is the determined relationship between transition energy and degree of signal depression resulting from the introduction of CO₂ to the plasma. Attempts to enhance the emission signals of non-metals by introducing H₂ into a He MIP are discussed. The inadequacy of excitation temperature, ionization temperature, rotational temperature, and electron number density measurements to determine the effect of CO₂ on the excitation characteristics of a He MIP is also described. However, application of kinetic theory and a recently developed theory on charge transfer allows a reasonable series of mechanisms to be developed that describe the excitation processes of a He MIP to which supercritical CO₂ is added. The remainder of this work describes a direct interface between a supercritical fluid extraction (SFE) vessel and an Ar MIP for the purpose of element selective detection. The response of the plasma to the introduction of sample via SFE at a variety of extraction temperatures, pressures, and sample concentrations is presented. / Ph. D.