Browsing by Subject "Gas chromatography"
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Item A Gas Chromatographic Method to Determine Sorption Isotherms for Biomedical Polymers(Texas Tech University, 1977-12) Chen, HsienThis study is concerned with the development of a methodology whereby inverse gas-liquid chromatography can be utilized as an analytical tool to determine the sorption isotherms of chemical sterilants for biomedical polymers. Cellulose acetate and poly (vinylidene chloride/vinyl chloride) copolymer were successfully investigated with regard to their potential to adsorb isopropyl alcohol and aqueous solutions of formaldehyde and glutaraldehyde. Since those sterilants can be retained by the polymer matrix, it is important that their sorption characteristics can be understood. Otherwise, toxic levels of the sorbed chemical can be released into the biosphere after the polymer has been implanted into the human body. Inverse chromatography was found to be well suited for this type of study because of its speed, accuracy, and wide range of applicability. Moreover, the data obtained with this technique correspond to infinite dilution, or the low PPM concentration range so important in the removal of the last vestiges of the chemical sterilants.Item Development, validation, and application of cholesterol determination method for meat and poultry products using gas chromatography(2010-12) Dinh, Thu T. N.; Thompson, Leslie D.; Brooks, Chance; Galyean, Michael L.; Boylan, Lee M.; Patterson, KristineMichael Brown and Joseph Goldstein, two Nobel laureates, declared cholesterol to be the most highly decorated small molecule in biology, with 13 Nobel Prizes awarded to scientists dedicating their professional careers to cholesterol research. Windaus first determined cholesterol with using digitonin in 1910, followed by Grigaut with a colorimetric method using Liebermann-Burchard reaction in 1911. The development of innovative technologies and analytical instruments has allowed for incredible specificity, sensitivity, accuracy, and precision of cholesterol determination. The AOAC Official Method 994.10 employing GC-FID is currently used in most commercial laboratories for routine analysis of cholesterol in foods. Although significantly modified by employing direct saponification, it is still costly, time-consuming, and labor-intensive. The primary objectives of the present study were to refine the analytical conditions for improved performance, develop a written procedure, and determine intra- and inter-laboratory performances of a newly developed method using the AOAC-required performance measurements. Cholesterol was liberated from meat and poultry samples and was detected using GC-FID at a retention time of 11.96 min. Using 0.005 mg of 5α-cholestane/mL as internal standard, the linearity of the standard curve was determined for peak ratio and standard concentrations of 0.008 to 0.020 mg of cholesterol/mL with a coefficient of determination of 0.995 and a response factor of 0.66 (CV = 3.84%). The limits of detection and quantitation were 1.24 and 4.00 mg/100 g, respectively. Cholesterol was stable in the toluene extract when stored for up to 6 d under refrigeration before GC analysis as demonstrated by high precision (0.92 to 2.69% CV) and accuracy (93.24 to 100.56% recovery) of the results. This method was proved to be more accurate and precise compared with results from two commercial laboratories using the AOAC 994.10 method. The new method was also tested for robustness in two ruggedness trials and was collaboratively validated. This method has now been routinely applied to update cholesterol content of meat and poultry in the USDA National Nutrient Database for Standard Reference with high reliability and productivity. Data from 363 meat and poultry samples with 799 replicates showed that 91.5% of total samples were measured with CV of less than 6% and Horwitz ratios of less than 2.0. Collective data for a meat homogenate, SRM1546 (certified reference material), indicated that most of measured concentrations were within the certified range.Item Gas chromatographic analysis of oxygenated organic compounds in the presence of water(Texas Tech University, 1968-06) Lee, Won-KyooNot availableItem Investigations in capillary liquid chromatography(Texas Tech University, 1997-08) Mo, YouwenNot availableItem Phthalates and polybrominated diphenyl ethers in retail stores(2012-12) Urquidi, Jorge Rodolfo; Xu, Ying (Assistant professor); Siegel, JeffreyRetail stores are an environment with a rich diversity of toxic chemicals typically found in consumer products. Among these chemicals, semi-volatile organic compounds (SVOCs) are an important class with great health concerns. Phthalates and polybrominated diphenyl ethers (PBDEs) are high production volume SVOC chemicals pervasively used in plastics and other consumer products. Exposure to them may cause serious adverse health effects, including endocrine disruption. They, however, have not been widely studied in retail environments. In this study, indoor air samples were collected from 15 retail stores in Austin, TX and University Park, PA. Some of these stores were revisited on different temperate seasons to account for weather variability. Indoor concentrations of the most ubiquitous pollutants were correlated with several building characteristics, including retailer type, temperature, and building use characteristics. Collected data shows a wider variety of phthalates and PBDEs, as well as higher indoor airborne concentrations for large department stores as compared to grocery stores, which typically have fewer sources in comparison.Item The effect of structural modifications on solvent interactions with siloxane polymers(Texas Tech University, 1978-05) Chen, Ko-ChiGas-Liquid chromatography (GLC) was used to investigate the sensitivity of GLC data to structural modification in a series of alkyl- and fluoroalkyl- substituted siloxane polymers. Experimental data at 55°C, 70°C, 85°C and essentially atmospheric pressure for each solute in the siloxane polymer systems at infinite dilution are presented. Infinite-Dilution pseudo activity coefficients (Ω∞) and thermodynamic quantities (e. g., ∆Hm, ∆Gm, ∆Sm) were obtained from data taken at 55°C, 70°C and 85°C. The significance of the results to melting transition in polymers, glass transition in polymers, polymer solubility, and the effect of polymer structural modification with solubility are discussed. It is concluded that gas chromatography is a valuable tool for studying the structure of polymers and their interaction with compounds of lower molecular weight.