Characterisation Of Environmental Pollution By Gc-Ms Analysis Of Polycyclic Aroma Tic Compounds In Water And Soil

Abstract

Polycyclic aromatic hydrocarbons (PAHs) have long been known to pose health risks in humans and. have become one of the major environmental issues. Coal tar products, refined petroleum products and lubricating oils are among the anthropogenic sources, which contain highly toxic substances of which benzo [ a] pyrene and dibenzo[ a,h]anthracene are the most potent carcinogens. Sensitive and reliable chemical analyses of contaminated soil and water are imperative for health risk assessments and chemical fingerprinting. The development of techniques that can determine the pollution source is motivated in part by the clean-up costs, legal fees, and fines incurred by the polluter. In this thesis, direct solid-phase microextraction (DISPME), followed by capillary gas chromatography ( GC) and mass spectrometry (MS) in the selected ion storage (SIS) mode was investigated for the determination and characterisation of P AHs in aqueous samples. The SPME method of extraction is also compared to a traditional liquid-liquid extraction method that was based on USEPA method 8270. It was found that several factors affected the extraction efficiency with a single stage SPME extraction, such as the degree of alkylation, fibre condition, absorption time, sample pH, sample matrix, sample temperature, agitation method, etc. The technique of multiple extractions (MESPME) was investigated and found to compensate for variations in analytical conditions or sample matrix. The suitability of the method for health risk assessments was investigated. The results were acceptable for this purpose because the limits of detection were estimated at the pg/cm3 levels that were considerably lower than the health risk-based guideline concentrations (10-6 cancer risk) for drinking water specified by the United States Environmental Protection Agency (USEP A). The guideline concentration for dibenz[ a,h ]anthracene (the most potent carcinogen) is for example 0.0092 ng/cm3 compared to a detection limit of 0.0045 ng/cm3 achieved with the SPME-GC/MS method. Detection limits for the other carcinogenic P AHs were also found to be lower than the USEP A guideline concentrations. The method was also developed to include the quantification of alkyl-PAHs, which is important for interpretative methods such as chemical fingerprinting (source identification). For this purpose, detection limits of at least 0.0 I ng/cm3 are required for individual P AHs. The SPME extraction method used in conjunction with GC/MS was found to be sensitive enough for this purpose with detection limits lower than 0.01 ng/cm3 for all the PAHs. The method was in many respects’ superior to traditional extraction methods. A headspace SPME (HSSPME) method, followed by GC/MS, was developed for the screening of soil samples. Vapor pressures of target analytes were determined using a capillary GC method to identify environmentally important components with a sufficiently high vapor pressure to be analysed in the headspace mode. The method was optimized under nonequilibria um conditions with simplicity and automation in mind and does not require any extraction procedure or sample preparation, other than grinding, drying and homogenizing. The analytical performance and the significance of the results for the purpose of chemical characterisation, source discrimination, determination of individual isomer distributions and the calculation of source and weathering ratios, are discussed. The SPME method of extraction was also compared to the relatively new extraction technique known as Pressurised Liquid Extraction (PLE). HSSPME was found to be a very efficient and sensitive technique for the confirmation of PAHs of up to four-ring structures and suitable for a tiered and adaptive approach. The selective extraction and analysis techniques that have been developed in this thesis were finally used to develop diagnostic ratios, which can be used to trace contamination in the environment to its source. The successful use of the analytical data to match the chemical patterns of target analytes with potential sources was shown.