Characterization of Polar Carbonaceous Particulate Matter Using Liquid and Gas Chromatography with Mass Spectrometry.

摘要

Polar organic compounds, due to their reactivity, volatility, water-solubility and surface activity, may play a major role in the atmospheric chemical and physical processes. A significant portion of organic carbon (presumably polar) in atmospheric particulate matter (PM) has not been characterized due to the lack of sensitive analytical methods or inappropriate sample preparation. This dissertation, therefore, focuses on the development of analytical methods for a characterization of polar organic compounds that can be encountered in PM (e.g., aldehydes, carboxylic acids, high molecular weight compounds).;In order to achieve a sensitive detection for aldehydes in PM, a method using chemical derivatization and solid phase micro-extraction (SPME) was developed. The optimized SPME method provided detection limits, which are two orders of magnitude lower than those of the US EPA 556 traditionally used method for all aldehydes (including aliphatic and aromatic aldehydes and dialdehydes). The newly developed SPME method also minimized the analytical artifacts (i.e., evaporative losses of volatile analytes) observed using the traditional sample preparation.;The sample preparation and trace analysis method for carboxylic acids occurring in air PM were optimized. Due to the complex sample matrix, the liquid chromatography/mass spectrometry (LC/MS) method with electrospray ionization encountered problems with ion suppression and would require additional sample purification. Gas chromatography/mass spectrometry (GC/MS) with prior derivatization was found to be a more efficient and sensitive technique for the majority of analytes. Extraction recoveries of carboxylic acids from diesel exhaust PM, urban PM and wood smoke PM depended on the strength of the used method (hot pressurized water and Soxhlet solvent extractions). The extraction efficiency may model the availability of carboxylic acids for further reactions in PM.;Extraction studies to investigate the decomposition of oligomers and formation of aldehydes during the sample preparation were performed. The results provided indirect evidence for presence of oligomers with a "dialdehyde backbone" in PM.;For recognition of "unknown" non-volatile HMW species in PM, a novel approach which involved a sequential thermal extraction (TE) followed by pyrolysis (Py) of PM constituents with on-line GC/MS analysis was developed. Using TE/Py-GC/MS, it was revealed that PM may contain a significant portion of biopolymers (i.e., proteins, polysaccharides, nucleic acids, lipids) as well as large non-volatile hydrocarbons. The identification of these compounds and their association with HMW species was possible due to the removal of low molecular weight structures prior to the pyrolysis.