AN ABSTRACT OF THE THESIS OF Shane W. Monares for the degree of Honors Baccalaureate of Science in Chemistry presented on May 25, 2010. Title: Adapting the Methylene Blue Sulfide Detection Method for Use in a Microfluidic in-situ Monitoring Device.

Sulfide is an important species to measure in environmental water samples. The spectrophotometric detection method for reduced sulfur species (sulfide) based on generation of methylene blue was adapted to work in an apparatus utilizing microfluidic PDMS mixing and observation cells with flow channels in the 100 µm range. The benefits of the system include the use of low volumes of reagents and sample, generation of low volumes of waste, and the possibility of adaptation to in-situ measurements with a submergible, microfluidic sensing device. The calibration equation for the detection of sulfide with this method is [S(-II)] = (Absorbance – 0.0147)/0.0045, where the sulfide concentration is in micromolar. The detection limit for this method was found to be 1 µM, which is comparable to conventional methods. Topics explored include: sulfide standard stability and protection from loss due to oxidation and volatilization, preparation and stability of a single reagent with multiple components, microfluidic apparatus development, and the calibration of the method for sulfide concentrations. Key Words: sulfide detection, microfluidics, analytical chemistry, monitoring device