Fiber optic sensors and spectrometry for the detection of volatile gem-polyhalogenated hydrocarbons Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/3j333566k

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  • A fiber optic fluorometer utilizing a double-fiber optic probe was constructed. The absolute fluorescence signal and effective collection efficiency are approximately one fifth those of typical cuvette fluorometers and agree with those predicted by theory. A quinine sulfate calibration curve shows linearity from a detection limit of 10 pg/mL to 10 μg/mL. Single- and double-fiber probe configurations were also compared. The double-fiber configuration provided better detection limits due to its superior signal-to-background ratio. A discussion of sensor methodology for the monitoring of reaction intermediates is presented and a simple kinetic model for predicting the time dependent response of such sensors is developed. Two possible mechanisms for the Fujiwara reaction with chloroform are discussed. The effect of pyridine, water, and base concentrations on reaction kinetics was evaluated to develop single-phase Fujiwara reagent mixtures for both fluorometric and spectrophotometric determinations of chloroform. A unique "continuous-exposure" apparatus allowing vapor phase transport of chloroform from an aqueous sample to a conventional cuvette was constructed. The spectrophotometric detection limit for chloroform is 11 ng/mL and the method was shown to be suitable for the analysis of tap water. Two fiber optic chemical sensors (FOCS) for the detection of chloroform were developed. An aliquot of the optimized fluorometric reagent solution is held in contact with the fiber optic probe within a light-tight enclosure and is isolated from a bulk sample by a trapped headspace. One FOCS utilizes 1.3 mL of reagent held in a reservoir and the other utilizes a 10-μL drop of reagent suspended on the sensing tips of the fiber optic probe. Chloroform vapor from the sample migrates into the FOCS and reacts with the reagent to produce a fluorescent reaction intermediate which is monitored at 590 nm; the rate of increase in the fluorescence signal is related to chloroform concentration. Both FOCSs give detection limits better than 0.1 ng/mL. The response and total measurement times are comparable for the two FOCSs, and the duration of the linear response is limited by inner-filter effects. The response to a number of volatile GPHHCs including the trihalomethanes are reported. Analyses of tap water for chloroform with the reservoir FOCS and GC/MS were in excellent agreement.
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