Sample preparation in environmental organic analysis

Barnabas, Ian Joseph (1996) Sample preparation in environmental organic analysis. Doctoral thesis, University of Northumbria at Newcastle.

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Abstract

Sample preparation in organic analytical chemistry is often the most important stage in the entire analysis procedure. However, there has been little development in the techniques used in over one hundred years and solvent extraction is still the method of choice. Unfortunately, this is time-consuming and creates large quantities of organic solvents which are harmful to the environment. The work presented here investigates the use of several new instrumental sample preparation techniques including, supercritical fluid extraction, solid-phase extraction, solid-phase microextraction and microwave assisted extraction. All of the techniques significantly reduce organic solvent consumption whilst allowing greater sample throughput through faster extraction and a greater scope for automation. Supercritical fluid extraction, using carbon dioxide as a solvent, dominates the project and has been used to extract pesticides from water, both directly and in combination with solid-phase extraction. Direct extraction proved ineffective due to the extensive extraction time required, although the combined approach is shown to allow selective extraction of different classes of pesticides and herbicides to be performed by alteration of the supercritical fluid conditions. In addition, solid-phase microextraction technology, which requires no organic solvents, has been used to extract herbicides from the same matrix. After the optimization of operating conditions, the technique was capable of the automated extraction and analysis of the analytes at a concentration of 0.1 ýtg 1-1. Supercritical fluid extraction protocols have also been developed which are capable of extracting similar concentrations (if not greater) of polycyclic aromatic hydrocarbons from soils as compared to traditional Soxhlet extraction, with a significant reduction in the overall extraction time. The technique was also compared with a microwave assisted extraction method which allows the simultaneous extraction of multiple samples. The optimization of operating parameters in both techniques was facilitated by the use of experimental design procedures capable of interpreting data obtained from experiments involving the simultaneous alteration of operating variables. Each system was found to have their strengths and weaknesses which are discussed, however, in both instances the soil matrix was found to play an important role in extraction efficiency. Further studies involving the supercritical fluid extraction of pesticides from various characterized soils concluded that the soil matrix significantly affected the overall extraction performance which was found to be particularly dependent on soil organic matter.

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