The chromatographic properties of various silicone stationary phases for capillary gas chromatography have been extensively studied, yet the properties of nonsilicone phases have not been so well investigated. The most popular nonsilicone phases are the high molecular weight polyethylene glycols (HMW PEG) which are commercially available in a wide range of molecular weights, cross-linkable and uncross-linkable (Carbowax 2OM and 4OM, the Superox series, etc.). Their most outstanding features are their unique polarity and selectivity; for this reason these phases are widely used in the analysis of aqueous solutions, essential oils, and perfumes. Unfortunately HMW-PEG's are very sensitive to slight differences in preparation and handling procedures which can cause analyses to differ with each laboratory, each column, and even each use. HMWâ PEG's also suffer from low temperature stability, a high minimum allowable operating temperature, and have lower diffusion coefficients than silicone phases. This study examines the efficiency differences of eight columns differing only in immobilization procedure and added functional groups. Comparison is made using HETP versus u and separation number (TZ) versus u curves. These curves offer important information, in particular, the effect of carrier gas, u, column operating temperature, degree of cross-linking, and cross-linking temperature on chromatographic efficiency and separation number. In addition, the contributions of the CL (resistance to mass transfer in the liquid phase) and DL (diffusion coefficient in the liquid phase) terms in the Golay equation are calculated [1]. Solids at room temperature, PEG stationary phases undergo a solid-liquid phase transition within their useful temperature range. The effect of this transition on the chromatographic properties is investigated using efficiency, separation number, capacity ratio, and retention index versus temperature curves. Four more columns, in addition to the eight mentioned above, demonstrate the influence of end-groups and the molecular weight of the stationary phase on the phase transition temperature range. / Master of Science

Wide-bore, fused-silica capillary columns can be an excellent replacement for packed columns in many cases. They can provide higher surface inertness and thermal stability, as well as higher efficiency or speed of analysis. Wide-bore, open-tubular (WBOT) columns with thick films have higher sample capacities than conventional narrow-bore capillary columns and can be used in unmodified packed-column gas chromatographs. The majority of gas chromatographic analyses are still performed using packed columns. Many chromatographers associate open-tubular columns exclusively with split injection, often perceived as less repeatable or quantitative. Also, many packed-column methods use application-specific stationary phases which are not readily available on capillary columns. WBOT columns with standard phases can often be substituted due to higher available efficiencies. While several studies have been published on qualitative differences, there is little comparative quantitative data available on O.53â mm I.D. and packed columns. / Master of Science

A ready-to-deploy implementation of microfabricated gas chromatography (microGC) system characterized for detecting hazardous air pollutants (HAPs) at parts-per-billion (ppb) concentrations in complex mixtures has been described. A microfabricated preconcentrator (microPC), a MEMS separation column with on-chip thermal conductivity detector (microSC-TCD), the flow controller unit, and all the necessary flow and thermal management as well as user interface circuitry are integrated to realize the fully functional microGC system. The work reports extensive characterization of microPC, microSC and micro]TCD for target analytes: benzene, toluene, tetrachloroethylene, chlorobenzene, ethylbenzene, and p-xylene. Limit of Detection (LOD) of ~1 ng was achieved, which corresponds to 10 min sampling time at a flow rate of 1 mL/min for analyte present at ~25 ppbv concentration. An innovative method for generating very sharp injection plugs from the microPC even in the presence of flow sensitive detectors like micro]TCD is described. A one-to-one comparison between microGC system and conventional Automated Thermal Desorption-Gas Chromatograph-Flame Ionization Detector (ATD GC-FID) system for real gasoline samples in simulated car refueling scenario is reported. / Master of Science

The experimental parameters controlling the rate and mechanism of the decomposition of compounds and the products formed, in a moving carrier gas stream were investigated. The parameters studied included the effects of pyrolysis temperature, sample size, sample weight, flow rate of the carrier gas, the method of introducing the sample into the pyrolysis unit. An apparatus for pyrolysis-gas chromatography, using tho commonly used boat and furnace technique, was developed. Commercial grade sodium dodecylbenzene sulfonate was chosen for a model compound. The optimum conditions for the pyrolysis-gas chromatographic analysis of this material were established by the careful study of the experimental parameters. The most serious limitations to this method of pyrolysis-gas chromatography appeared to be the strong dependence on the sample size and tho dependence on pyrolysis temperature, i.e., on the rate at which the sample was brought to the pyrolysis temperature. As the size of the sample was increased the amount of residue in the boat also increased. Also, although the majority of the sample was pyrolyzed at 580°C the amount of residue would decrease as the temperature was raised to a maximum of 710°C. A certain amount of residue always remained in the boat. The residue can be explained as the product of secondary reactions occurring between the initial pyrolysis intermediates (free radicals) and the unpyrolyzed portion of the sample. In an attempt to eliminate these effects of secondary reactions a new technique of pyrolysis-gas chromatography by direct injection of solutions was developed. By handling the samples in dilute solution it was shown that a much smaller sample could be pyrolyzed such that the probability or secondary reactions was greatly reduced. Also the very small samples allow an apparent instantaneous heating of the samples to a given pyrolysis temperature. This approach offers a means of obtaining the simplest possible products from the pyrolysis of a compound, therefore offering a more accurate insight into the mechanism of the pyrolysis. These products then offer a means of establishing the structure of the original compound. Using this technique a method was developed for analyzing aqueous solutions containing the alkylbenzene sulfonates. This method provides not only a measure of the total detergent present but also differentiates between the various alkyl groups found in the commercial products. The alkyl groups form the 1-alkenes which can be easily identified chromatographically. The conditions for this analysis along with curves showing the products obtained from the pyrolysis of samples with both straight and branched alkyl groups are given. While the majority of the work done here was with aqueous solutions an attempt was made to determine the stability or some of the common organic solvents under such pyrolysis conditions. Those solvents studied were methylene chloride, chloroform, carbon tetrachloride, methanol, ethanol, and acetone. All of these solvents were round to be stable up to 500°C; however, at temperatures greater than this the decomposition of the solvents limits their use. The technique of pyrolysis-gas chromatography by direct injection or solutions was also applied to certain amino acids in ethanol-water solutions. The results were again much more accurate than those found with the boat technique. This technique was also shown to be useful in determining the structure of organic chelates bound to metal atoms. Solutions of copper II and chromium III acetyl-acetonates in chloroform were pyrolyzed and the product identified as acetylacetone. This offers a means of determining both the number and type of chelates bound to a given metal atom. / Ph. D.

This study concerns the effect of column temperature on selectivity in gas chromatography (GC). Reversal of peak elution order at different temperatures is observed when selectivity is sufficiently changed by changing the temperature. A study of homologous functional groups and the elution order of a test mixture was made at several temperatures, by keeping constant operating chromatographic parameters such as column head pressure, split ratio, sample concentration, injector and detector temperature. The homologous series studied were esters, carboxylic acids, ketones and alkanes. The stationary phases used were Carbowax (Supelcowax 10), and 5% diphenyl and 95% dimethyl silicone ( HP Ultra 2). The identification of each compound was confirmed by two methods : comparing retention times, and spiking the sample. The results of an investigation for accurately determining the dead time is also presented. The experimental results of using 10% methane in helium and the results of a theoretical model based on Poiseuille's equation were studied and compared. It is concluded that dead time calculations are a major source of error for the calculations in this work. In addition, a derived thermodynamic equation based on the Van't Hoff equation was obtained and used to calculate the molar enthalpy and entropy of compounds over a range of temperatures. The experimental thermodynamic values were compared with the theoretical values obtained from the Clausius- Clapeyron equation. From the data obtained, a graph of In k' (retention factor) versus 1/ temperature for a homologous series, known as a Van't Hoff plot, predicts a reversal of elution order where an intersection of two lines occur. Selectivity of the stationary phase has changed solely due to temperature effects. This can only occur when different solute/solvent interactions are present. This work is an attempt to predict when peak inversion should occur based on the Van Hoff's plot. Experimental result are presented that confirm the prediction. / Master of Science

Thesis (Ph. D.)--Pennsylvania State University, 1968. / Includes bibliographical references.

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous contaminants and are mostly products of the incomplete combustion of organic material. PAHs are often found in environmental samples as a complex mixture of isomers. In addition, the same sources that produce complex PAH mixtures also produce other poorly characterized mixtures of organic compounds, commonly referred to as an unresolved complex mixture (UCM), that act as matrix interferences in the chromatographic analysis of samples. Conventional one-dimensional chromatographic techniques, such as gas chromatography coupled to mass spectrometry (GC/MS), are not sufficient for the analysis and quantitation of complex PAH mixtures present in environmental samples due to the high degree of overlap in compound vapor pressures, boiling points, and mass spectral fragmentation patterns. Therefore, the separation and quantitation of complex mixtures of individual PAH compounds in environmental samples requires high chromatographic resolution. Comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC��GC/ToF-MS) was used for this study. GC��GC/ToF-MS uses two different gas chromatographic columns, with different separation mechanisms, for the analysis of complex environmental samples. In theory, the peak capacity in GC��GC/ToF-MS is equivalent to the product of the individual peak capacities of each column used. However, in practice, this is rarely obtained because of the existing correlation between the two GC columns used. This dissertation is a compilation of three studies related to analytical method development for the identification and quantitation of complex PAH mixtures (including parent-PAHs, alkyl-PAHs, oxy-PAHs, nitro-PAHs, thio-PAHs, chloro-PAHs, bromo-PAHs and PAHs with molecular weight higher than 300 Da) that may be present in environmental samples using novel column combinations in GC��GC/ToF-MS. The use of a liquid crystal column (LC-50) in the first dimension, followed by a nano-stationary phase column (NSP-35) in the second dimension, was evaluated for the separation of a standard PAH mixture containing 97 different PAHs. Two standard reference materials purchased from NIST (NIST SRM1650b ��� Diesel Particulate Matter and NIST SRM1975 ��� Diesel Extract) were used, after extraction and cleanup, for method validation and comparison between the commonly used non-polar �� polar column combination and the LC-50 �� NSP-35 column combination with high orthogonality. As part of the method validation, an aliquot of NIST SRM1975 (Diesel extract), without sample cleanup was also analyzed for PAHs, showing that the LC-50 �� NSP-35 column combination was accurate (with an average absolute percent difference of approximately 30%) for the identification and quantitation of complex PAH mixtures in environmental samples, with reduced sample preparation prior to analysis. In addition, the LC-50 �� NSP-35 column combination was used for the analysis of PAHs sorbed to polystyrene pellets deployed in an urban bay area as passive water samplers because one-dimensional GC/MS was ineffective due to the presence of a strong unresolved complex mixture (UCM) and matrix interferences. / Graduation date: 2013 / Access restricted to the OSU Community at author's request from Dec. 27, 2012 - June 27, 2013

This research contributes to worldwide efforts to miniaturize one of the most powerful and versatile analytical tools, gas chromatography (GC). If a rapid, sensitive and selective hand-held GC system is realized, it would have a wide range of applications in many industries and research areas. As a part of developing a hand-held GC system, this research focuses on the separation column, which is the most important component of a GC system. This thesis describes the development of a miniature separation column that has low thermal mass and an embedded heating element for rapid thermal cycling. The worlds first thin polymer film (parylene) GC column has been successfully developed. This thesis includes: first, a study of theoretical column performance of rectangular GC column; second, the design optimization of parylene column and embedded heating element; third, the development of new processes such as parylene micromolding and stationary phase coating technique for parylene column; fourth, the fabrication of parylene GC column with an embedded heating element; and lastly, the testing and evaluation of parylene GC column through GC analysis.

The determination of carbon monoxide is also possible by trapping CO on preconditioned molecular sieve and thermal desorption. Analysis in this case is performed by gas chromatography/mass spectroscopy, although the trapping technique is applicable to other suitable GC techniques.

Dissertation submitted in fulfilment of the requirements for the Masters Degree in Technology: Chemistry, Durban University of Technology, 2009. / The activity coefficients at infinite dilution ( γ13 ) were calculated for alkanes, alkenes, cycloalkanes, alkynes, ketones, alcohols and aromatic compounds from gas liquid chromatography (glc) measurements at three temperatures (303.15 and 313.15 and 323.15) K. The γ13 values were calculated from the retention data for two ionic liquids (ILs) with the same cation but different anions. The ionic liquids: [methyltrioctylammonium bis(trifluoromethylsulfonyl)imide and methyltrioctylammonium thiosalicylate] were used as the stationary phase. The γ13 data for methyltrioctylammonium thiosalicylate were higher than for methyltrioctylammonium bis(trifluoromethylsulfonyl)imide. For each temperature and each ionic liquid, γ13 values were determined for two columns and the average γ13 values were used for the calculation of the partial molar excess enthalpies at infinite dilution, H E 1 Δ , using the Gibbs-Helmholtz equation. Graphs of In γ13 vs 1/T were plotted to determine H E 1 Δ at T = 303.15 K. The selectivity, S12 , value for the hexane/benzene separation was calculated from the ratio of the avarage γ13 values to determine the suitability of the ILs as an entrainer for extractive distillation in the separation of aromatic and aliphatic compounds.The S12 values were also compared to the literature values for other ionic liquids. It was found that the longer chain alkyl group attached to the cation or anion gave lower S12 values. Both ILs have S12 values greater than one and in theory can be used as an entrainer for the hexane/ benzene separation. The capacities at infinite dilutions, k1 , were also calculated from the inverse of the avarage γ13 values for each IL at each temperature. / National Research Fund; Postgraduate Development and Support Directorate.