Date of Award


Document Type

Open Access

Degree Name

Bachelor of Science






In this research a flow injection (FI) apparatus with a laser-based detector is characterized using three chemical systems and the results are compared to those obtained by other researchers using conventional instrumentation. Each chemical system involves Methylene Blue (MR), a common redox indicator. A 670-nm diode laser is used as the excitation source, and the resulting fluorescence is measured. In the first system, MB is formed as a product of the reaction of N,N-dimethylphenylenediamine (DMPD), iron (lll) and sulfide in the presence of acid. A three-line FI manifold is employed. The amount of sulfide in water samples, including a complicated wastewater matrix, is determined indirectly by measuring the fluorescence intensity of the MB produced in the or-line reaction. We perform the reaction under less corrosive conditions than previous researchers, and are able to make sensitive measurements (20-ppm limit of detection). For the second system under study, MB reacts with glucose, a reducing sugar, to produce the colorless leuco-MB. This system is not observed on-line due to the lack of sufficient quantities of dissolved oxygen in the flow stream. For the third system, ethanol reacts with NAD* in the presence of dehydrogenase, and the NADH produced can subsequently react with MB to form Leuco-MB. A decrease in MB fluorescence is observed with decreasing concentration of ethanol. Altl10ugh the on-line reaction can be detected successfully, a linear relationship between the injected concentration of ethanol and signal size has not been observed yet.

Included in

Chemistry Commons



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