| Summary: | Thesis (M. Eng.)--Harvard-MIT Division of Health Sciences and Technology, 2005. === Includes bibliographical references (leaves 92-95). === Breath analysis has potential to become a new medical diagnostic modality. In this thesis, a method for the analysis of human expired breath was developed using gas chromatography-mass spectroscopy. It was subsequently adopted for gas chromatography-differential mobility spectroscopy, a modality not previously applied to this problem. Tedlar bags and solid-phase microextraction were used for breath sampling and concentration prior to analysis. Four fiber coatings were evaluated with respect to selectivity and sensitivity; extraction time, gas chromatography temperature programming, and sample storage stability were explored for optimization. The method entails extraction and preconcentration with a polydimethylsiloxane-divinylbenzene coated fiber for 30 min at 37⁰C, and extraction profiles for several compounds demonstrate competitive adsorption. 120 compounds were identified in breath with response variability between 23 - 117% about mean values. Feasibility of differential mobility spectroscopy for breath analysis was established, and this method will be the basis for future investigations on the diagnostic potential of breath analysis. === by William Merrick. === M.Eng.
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