Increasing consumer awareness of food safety issues requires the development of highly sophisticated techniques for the authentication of food commodities. The food products targeted for falsification are either products of high commercial value or those produced in large quantities. For this reason, the present investigation is directed toward the characterization of coffee samples according to geographical origin attributes. In addition, the current examination is focused on the identification of particular marker compounds that compose the volatile and semivolatile aroma fraction of flavoured and dessert coffees. The conducted research involved the development of a rapid headspace solid phase microextraction (HS-SPME) – gas chromatography – time-of-flight mass spectrometry (GC-TOFMS) method for the verification of geographical origin traceability of coffee samples. As opposed to the utilization of traditional univariate optimization methods, the current study employs the application of multivariate experimental designs to the optimization of extraction-influencing parameters. Hence, the two-level full factorial first-order design aided in the identification of two influential variables: extraction time and sample temperature. The optimum set of conditions for the two variables was 12 min and 55 oC, respectively, as directed by utilization of the Doehlert matrix and response surface methodology. The high-throughput automated SPME procedure was completed under optimized conditions by implementing a single divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) metal fiber with excellent properties of durability, which ensured the complete analysis of coffee samples in sequence. The coffee sample originating from an authentic Brazilian coffee producing region and characterized by rich volatile and semivolatile chromatographic profiles was selected as a reference starting point for data evaluation. The combination of the retention index (RI) system using C8-C40 alkanes and the mass spectral library search was utilized for the confirmation of analyte identity in this reference sample. Twenty-nine volatile and semivolatile compounds selected across the wide range of GC chromatogram were then evaluated in terms of chromatographic peak areas for all samples that are to be submitted to this classification study. The semiquantitative results were submitted to statistical evaluation, namely principal component analysis (PCA) for the establishment of corresponding geographical origin discriminations.

Membrane extraction with a sorbent interface (MESI) is a sample preparation technique with a rugged and simple design allowing for solvent-free, on-line performance. When coupled to gas chromatography (GC), MESI is an extremely promising tool for the analysis of volatile organic compounds (VOCs), as it is selective and sensitive for detecting trace levels of analytes. A new calibration method to be used with the MESI technique is presented herein. The aim of this project was to characterize and quantify the biomarker ethylene in human breath and plant emissions. The MESI-GC system was optimized, and an external calibration curve for ethylene standard was obtained. Qualitative measures were obtained from emissions of the higher plant Arabidopsis thaliana. The dominant calibration method was validated by examining changes in mass transfer trends when flow and temperature conditions were altered. Finally, the dominant calibration method was used to quantify ethylene in real human breath samples from non-smoking and smoking volunteers. Results were consistent with those reported in literature. These findings suggest that the dominant calibration technique is a useful tool for monitoring ethylene in human breath and Arabidopsis.

Increasing consumer awareness of food safety issues requires the development of highly sophisticated techniques for the authentication of food commodities. The food products targeted for falsification are either products of high commercial value or those produced in large quantities. For this reason, the present investigation is directed toward the characterization of coffee samples according to geographical origin attributes. In addition, the current examination is focused on the identification of particular marker compounds that compose the volatile and semivolatile aroma fraction of flavoured and dessert coffees. The conducted research involved the development of a rapid headspace solid phase microextraction (HS-SPME) – gas chromatography – time-of-flight mass spectrometry (GC-TOFMS) method for the verification of geographical origin traceability of coffee samples. As opposed to the utilization of traditional univariate optimization methods, the current study employs the application of multivariate experimental designs to the optimization of extraction-influencing parameters. Hence, the two-level full factorial first-order design aided in the identification of two influential variables: extraction time and sample temperature. The optimum set of conditions for the two variables was 12 min and 55 oC, respectively, as directed by utilization of the Doehlert matrix and response surface methodology. The high-throughput automated SPME procedure was completed under optimized conditions by implementing a single divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) metal fiber with excellent properties of durability, which ensured the complete analysis of coffee samples in sequence. The coffee sample originating from an authentic Brazilian coffee producing region and characterized by rich volatile and semivolatile chromatographic profiles was selected as a reference starting point for data evaluation. The combination of the retention index (RI) system using C8-C40 alkanes and the mass spectral library search was utilized for the confirmation of analyte identity in this reference sample. Twenty-nine volatile and semivolatile compounds selected across the wide range of GC chromatogram were then evaluated in terms of chromatographic peak areas for all samples that are to be submitted to this classification study. The semiquantitative results were submitted to statistical evaluation, namely principal component analysis (PCA) for the establishment of corresponding geographical origin discriminations.

Membrane extraction with a sorbent interface (MESI) is a sample preparation technique with a rugged and simple design allowing for solvent-free, on-line performance. When coupled to gas chromatography (GC), MESI is an extremely promising tool for the analysis of volatile organic compounds (VOCs), as it is selective and sensitive for detecting trace levels of analytes. A new calibration method to be used with the MESI technique is presented herein. The aim of this project was to characterize and quantify the biomarker ethylene in human breath and plant emissions. The MESI-GC system was optimized, and an external calibration curve for ethylene standard was obtained. Qualitative measures were obtained from emissions of the higher plant Arabidopsis thaliana. The dominant calibration method was validated by examining changes in mass transfer trends when flow and temperature conditions were altered. Finally, the dominant calibration method was used to quantify ethylene in real human breath samples from non-smoking and smoking volunteers. Results were consistent with those reported in literature. These findings suggest that the dominant calibration technique is a useful tool for monitoring ethylene in human breath and Arabidopsis.

The ability to effectively analyze particulate matter (PM2.5) in air is becoming increasingly pertinent. Allen Goldstein of the University of California in Berkeley is studying the semi-volatile fraction of organic compounds in PM2.5 through the use of the thermal desorption aerosol gas chromatograph (TAG) system. However, as conventional GC does not provide adequate separation power, the development of comprehensive two-dimensional gas chromatography (GC × GC) was required. GC × GC works more effectively by utilizing a modulator that periodically traps and focuses analytes from a primary column onto a secondary column. This allows for the primary and secondary columns to separate the analytes based on two different properties. This report focuses on the continuing study and enhancement of a modulator designed by Ognjen Panić during his Masters project. Improving and testing the robustness of this dual stage modulator was originally the focus of this project. However, this study led to the development of a single stage modulator. In addition to that, the effect of modulator characteristics such as length of the restriction, total length of the modulator and wall thickness on the modulator performance were studied. A robustness test of the single stage modulator was also completed. Experiments conducted tested the characteristics of the new modulator to ensure it performed effectively and would satisfy the requirements of the TAG system. A study comparing the sensitivity of conventional gas chromatography and GC × GC was also preformed. The sensitivity of GC × GC was on average an order of magnitude better than that of 1D GC.

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (leaves 145-155).

The Nitrogen Phosphorus Detector is a sensitive, selective device used in gas chromatography. It responds selectively towards nitrogen and phosphorus containing organic compounds with detection limits in the picogram range. The detector is of great importance for the measurement of trace levels of drugs, pesticides and herbicides in biological matrices and the environment. There is, however, some dispute in the literature regarding the detector's response mechanism. The detector is based on a hydrogen-air diffusion flame. Two electrodes polarise the flame with a potential difference of about 200 V and the current through the flame is measured using an electrometer amplifier. The selectivity of the system relies on the presence of an alkali metal source, usually rubidium. In the presence of nitrogen- and phosphorus-containing organics, C~ and PO· anions are formed, yielding a current which is the measured response. It has been suggested that this selective response arises from a charge transfer reaction between the rubidium excited states and ~ or PO· and P02• radicals. Using an AlGaAs diode laser, the rubidium excited state population can be modulated and the influence on detector current monitored. Rubidium resonance-enhanced ionisation, laser-induced fluorescence and emission spectroscopy have all been used to further probe the response mechanism of the detector. Results have demonstrated that during response the C~ radical concentration increases. In addition the diode laser can modulate the excited state rubidium concentration altering it by a factor of 2. However despite more that doubling the Rubidium excited state concentration no increase in detector response is observed. From these observations it has been concluded that the above mentioned charge transfer reaction plays little if any role in detector response.

No description available.

The aim of this work was to extend the theory of Everett and Cruickshank, for the determination of activity coefficients at infinite dilution, Y 13 (where 1 refers to the solute and 3 to the solvent), to accommodate solvents of moderate volatility, using the gas liquid chromatography (GLC) method. A novel data treatment procedure is introduced to account for the loss of solvent off the column, during the experiment. The method also allows us to determine the vapour pressure of the solvent. No auxiliary equipment is required, and the method does not employ the use of a presaturator. Further, the effect of a polar involatile solute is examined using various types of solutes. The activity coefficient was found to be independent of column packing and flowrate. Considering the volatile solvent, the systems investigated by the GLC method were straight chain hydrocarbons, (n-pentane, n-hexane and n-heptane), cyclic hydrocarbons (cyclopentane, and cyclohexane) and an aromatic compound, benzene. The systems were investigated at 2 temperatures, 280.15 K and 298.15 K. The results indicate a clear dependence of the activity coefficient on temperature. For the polar nonvolatile solvent, sulfolane (tetrahydrothiophene, 1,1 dioxane) was used. The systems studied were sulfolane + n-pentane, n-hexane, n-heptane, cyclopentane, cyclohexane, benzene, tetrahydrofuran, and tetrahydropyran. The systems were studied at one temperature, 303.15 K, due to the low melting point of sulfolane i.e. 301.60 K. Part of this study into the thermodynamics of solutions'\vas conducted at the Technical University of Warsaw, where the equilibria of sulfolane was studied using· two techniques, a dynamic solid-liquid equilibrium method (SLE), and an ebulliometriGI vapor-liquid method (VLE) . The main purpose of this was to apply solution theories to this data in order to predict the.activity coefficient at infinite dilution for the sulfolane mixtures. The systems measured using solid liquid equilibrium are sulfolane + tetrahydrofuran, or, 1,4-dioxane, or, I-heptyne, or, 1, 1, l,-trichloroethane, or, benzene, and cyclohexane. The results of these measurements were then described using various solution theories, and· new interaction parameters obtained. The vapour liquid equilibrium systems measured were sulfolane + I-heptyne, or, tetrahyrdofuran, or, 1,1, I-trichloroethane, and tetrachloromethane. Here as in SLE the results were described using solution theories. The results of both the VLE and SLE measurements were used in a multiple optimization procedure to produce new parameters for the interaction of sulfolane with various groups, using two group contribution method, DISQUAC and modified UNIFAC. The predicted activity coefficients compare well with the measured values using GLC. / Thesis (Ph.D.)-University of Natal, 1995.

The ability to effectively analyze particulate matter (PM2.5) in air is becoming increasingly pertinent. Allen Goldstein of the University of California in Berkeley is studying the semi-volatile fraction of organic compounds in PM2.5 through the use of the thermal desorption aerosol gas chromatograph (TAG) system. However, as conventional GC does not provide adequate separation power, the development of comprehensive two-dimensional gas chromatography (GC × GC) was required. GC × GC works more effectively by utilizing a modulator that periodically traps and focuses analytes from a primary column onto a secondary column. This allows for the primary and secondary columns to separate the analytes based on two different properties. This report focuses on the continuing study and enhancement of a modulator designed by Ognjen Panić during his Masters project. Improving and testing the robustness of this dual stage modulator was originally the focus of this project. However, this study led to the development of a single stage modulator. In addition to that, the effect of modulator characteristics such as length of the restriction, total length of the modulator and wall thickness on the modulator performance were studied. A robustness test of the single stage modulator was also completed. Experiments conducted tested the characteristics of the new modulator to ensure it performed effectively and would satisfy the requirements of the TAG system. A study comparing the sensitivity of conventional gas chromatography and GC × GC was also preformed. The sensitivity of GC × GC was on average an order of magnitude better than that of 1D GC.