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Noise analysis and numerical simulation in trace detection in molecular spectroscopy
Abstract
Development of sensitive methods for chemical analysis requires comprehensive understanding of the various experimental contributions to signal, interferences, and noise. This premise was applied to the development of multiphoton photoionization spectroscopy and optical polarimetry. For the former, two methods were attempted to improve performance in polar solutions. Auto-by-cross correlation was implemented as a signal processing scheme for quantifying transient signals, which included photoionization. Careful analysis of background fluctuations and signal-to-noise ratio behavior showed that, while the method itself was useful, certain peculiarities of its implementation with photoionization prevented full realization of the experimental goals. The second innovation for photoionization was to replace most of the polar solvent with nonpolar solvent, and sequester the polar solvent and analyte in the interior of a reverse micelle. Analysis of the background noise showed that noise reduction was excellent; solvent noise was reduced nearly to the level of heptane. The photoionization signal also decreased, such that no gain in signal-to-noise ratio was realized. However, it was shown that the microemulsion solutions offered a much better environment for analysis of aqueous-soluble compounds. It was also shown that microemulsions provided a means of performing analyses by photoionization that were otherwise impossible, such as at nonneutral pH. Numerical simulations were employed extensively in the development and evaluation of a laser-based optical polarimeter. Numerous simulations showed the optimum operating conditions for a Faraday rotator-based polarimeter, and provided an accurate means of evaluating previously published predictions. An experimental polarimeter was also constructed, and the source noise was manipulated to correspond with that of the simulations. It was shown that, when all experimental variables were taken into account, the simulations yielded very accurate predictions of polarimeter behavior.
Subject Area
Analytical chemistry
Recommended Citation
Johnson, Mitchell Evan, "Noise analysis and numerical simulation in trace detection in molecular spectroscopy" (1993). Doctoral Dissertations Available from Proquest. AAI9316671.
https://scholarworks.umass.edu/dissertations/AAI9316671