Author: Randall Monroe Hoes
Publisher:
ISBN:
Category : Gas chromatography
Languages : en
Pages : 366

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Author:
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Category : Power resources
Languages : en
Pages : 732

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Author: Carlos Andres Manzano
Publisher:
ISBN:
Category : Gas chromatography
Languages : en
Pages : 132

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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 (GCxGC/ToF-MS) was used for this study. GCxGC/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 GCxGC/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 GCxGC/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 x polar column combination and the LC-50 x 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 x 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 x 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.

Author: Mary C. Olson
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ISBN:
Category : Contaminated sediments
Languages : en
Pages : 62

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Author: Paul H. Miyares
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Category : Chromatographic analysis
Languages : en
Pages : 26

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Author: Wang Huiyong
Publisher:
ISBN:
Category : Extraction (Chemistry)
Languages : en
Pages : 232

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Polycyclic aromatic hydrocarbons (PAH) are important environmental pollutants originating from a wide variety of natural and anthropogenic sources. Because many of them are highly suspect as etiological agents in human cancer, chemical analysis of PAH is of great environmental and toxicological importance. Current methodology for PAH follows the classical pattern of sample preparation and chromatographic analysis. Sample preparation pre-concentrates PAH, simplifies matrix composition, and facilitates analytical resolution in the chromatographic column. Among the several approaches that exist to pre-concentrate PAH from water samples, the Environmental Protection Agency (EPA) recommends the use of solid-phase extraction (SPE). High-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS) are the basis for standard PAH identification and determination. Ultraviolet (UV) absorption and room temperature fluorescence detection are both widely used in HPLC, but the specificity of these detectors is modest. Since PAH identification is solely based on retention times, unambiguous PAH identification requires complete chromatographic resolution of sample components. When HPLC is applied to "unfamiliar" samples, the EPA recommends that a supporting analytical technique such as GC-MS be applied to verify compound identification and to check peak-purity HPLC fractions. Independent of the volume of extracted water, the approximate time required to separate and determine the sixteen "priority pollutants" (EPA-PAH) via HPLC is approximately 60min. If additional GC-MS analysis is required for unambiguous PAH determination, the total analysis time will reach 2-3 hours per sample. If the concentrations of target species are found to lie outside the detector's response range, the sample must be diluted and the process repeated. These are important considerations when routine analysis of numerous samples is contemplated. Parent PAH are relatively inert and need metabolic activation to express their carcinogenicity. By virtue of the rich heterogeneous distribution of metabolic products they produce, PAH provide a full spectrum of the complexity associated with understanding the initial phase of carcinogenesis. PAH metabolites include a variety of products such as expoxides, hydroxyl aromatics, quinines, dihydrodiols, dioepoxides, tetrols and water soluble conjugates. During the past decades tremendous efforts have been made to develop bio-analytical techniques that possess the selectivity and sensitivity for the problem at hand. Depending on the complexity of the sample and the relative concentrations of the targeted metabolites, a combination of sample preparation techniques is often necessary to reach the limits of detection of the instrumental method of analysis. The numerous preparation steps open ample opportunity to metabolite loss and collection of inaccurate data. Separation of metabolites has been accomplished via HPLC, capillary electrophoresis (CE) and GC-MS. Unfortunately, the existence of chemically related metabolic products with virtually identical fragmentation patterns often challenges the specificity of these techniques. This dissertation presents significant improvements in various fronts. Its first original component--which we have named solid-phase nano-extraction (SPNE)--deals with the use of gold nanoparticles (Au NPs) as extracting material for PAH. The advantages of SPNE are demonstrated for the analysis of PAH in water samples via both HPLC and Laser-Excited Time-Resolved Shpol'skii Spectroscopy (LETRSS). The same concept is then extended to the analysis of monohydroxy-PAH in urine samples via SPE- HPLC and In-Capillary SPNE-CE. The second original component of this dissertation describes the application of Shpol'skii Spectroscopy to the analysis of polar PAH metabolites. The outstanding selectivity and sensitivity for the direct analysis of PAH at trace concentration levels has made Shpol'skii spectroscopy a leading technique in environmental analysis. Unfortunately, the requirement of a specific guest-host combination--typically a non-polar PAH dissolved in an n-alkane-- has hindered its widespread application to the field of analytical chemistry. This dissertation takes the first steps in removing this limitation demonstrating its feasibility for the analysis of polar benzopyrene metabolites in alcohol matrixes.

Author: Wisam Abdulabbas Flayyih Al-Isawi
Publisher:
ISBN:
Category :
Languages : en
Pages : 94

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Gas chromatography-mass spectrometry (GC-MS) and liquid chromatography mass spectrometry (LC-MS) are powerful analytical techniques that combine the separation power in a stationary phase with the detection power of mass spectrometry. GCMS and LC-MS have gained dominant positions in identifying and quantifying different analyte species due to their high selectivity, high sensitivity, and high reproducibility. My research utilizes the analytical power of LC-MS and GC-MS to address two environmental issues: 1) Identification of biodegradation products of the ionic liquid 1- butyl-3-methylimidazolium chloride (BMIMCl) by an activated sludge microbial community using LC-MS and 2) identification and quantification of polycyclic aromatic hydrocarbons (PAHs) in the Kalamazoo River oil spill using GC-MS. Three major metabolites from BMIMCl biodegradation were identified, and their structures were confirmed using MS/MS and 1H-NMR techniques. Many PAHs were identified, and their concentrations were quantified in the Kalamazoo River oil spill area using GC-MS.

Author: Robert A. Baxter
Publisher:
ISBN:
Category : Gas chromatography
Languages : en
Pages : 34

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Author: IFEOLUWA GRACE. IDOWU
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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Concerns emanating from the presence of polycyclic aromatic compounds (PACs) in the environment especially as a yardstick for overall environmental health have been a challenge for several decades. Polycyclic aromatic compounds are a complex and structurally diverse class of compounds many of which can exist as isomers. Approaches to measure these compounds in environmental samples have relied on techniques based on gas chromatography coupled to mass spectrometry (GC/MS) at unit mass resolution. For example, the quantitation of the 16 US Environmental Protection Agency priority polycyclic aromatic hydrocarbons (PAHs) uses GC/MS and selected ion monitoring (SIM) of diagnostic m/z values of individual PAHs. Although this approach works well for the 16 priority PAHs, for more complex PACs, GC/MS in SIM mode is largely unreliable. Reasons for this include low selectivity of the SIM mode, insufficient chromatographic and mass resolution and the lack of commercially available authentic analytical standards. The overarching hypothesis of my thesis, therefore, is that more sophisticated chromatographic and MS techniques will provide more accurate measurements of PACs in the environment. The first advancement I made to the field of PAC research was the development of a one-dimensional GC coupled to MS method in the multiple reaction monitoring (MRM) to measure a suite of PACs. The method I developed was fully validated according to the EURACHEM guide - The Fitness for Purpose of Analytical methods and represents a significant improvement in the current SIM approach to quantitation of PACs in environmental samples. The second major advancement I made to the field of PAC research was the validation of a comprehensive 2D GC (GC×GC) high resolution time-of-flight (HR-TOF) MS method for the separation and quantitation of PACs. In this study I was able to exploit the increased peak capacity of the GC×GC system (relative to 1D) and the specificity of the HR-TOF/MS to quantify individual isomers of PAC compounds that were not attempted before. The methods I developed were paramount to the success of 2 other studies: (i) the GC/MS MRM method was used to understand the kinetics of PAH absorption to a highly sorptive medium that is used by industry to remediate the aquatic environment during/after an oil-spill and, (ii) the GC×GC-HR-TOF/MS was used in the detection of novel halogenated PACs in biological samples from the Alberta Oil Sands Region. The results of my work will have an impact and influence on future studies on source apportionment and chemical fingerprinting of crude-oil and will support much needed toxicological and monitoring studies of individual PAC isomers in the environment.

Author: Gaston Knobel
Publisher:
ISBN:
Category :
Languages : en
Pages : 137

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Chromatographic separation and quantification has been based on high-performance liquid chromatography-room temperature fluorescence detection (HPLC) and gas chromatography-mass spectrometry (GC-MS). Although chromatographic techniques provide reliable results in the analysis of OH-PAH, their experimental procedures are time consuming and expensive. Elution times of 30-60 minutes are typical and standards must be run periodically to verify retention times. If the concentrations of target species are found to lie outside the detector's response range, the sample must be diluted and the process repeated. On the other end of the concentration range, many samples are "zeroes," i.e. the concentrations are below detection limits. Additional problems arise when laboratory procedures are scaled up to handle thousands of samples under mass screening conditions. Under the prospective of a sustainable environment, the large usage of organic solvents is one of the main limitations of the current chromatographic methodology.