Masters Theses

Ming Huang

Keywords and Phrases

In situ NMR; Micro-sensor compound; PH measurement; Quantitative NMR; Temperature

Abstract

"The pH of an NMR sample can be measured directly by NMR experiments of signal intensities, chemical shifts, or relaxation time constants that depend on the pH. The 1H NMR peak intensities of the pH indicator phenolphthalein change as it changes from the OH-depleted form to the OH-rich form in the range of pH = 11.1 to 12.7. Because this range is rather small, another NMR technique was utilized based on 19F chemical shifts. The shift of F- in an aqueous solution of NaF changes in the alkaline range between pH = 11.0 and 14.0 and even more so in the acidic range between pH = 1.0 and 4.0. A new device made it possible for NMR samples to accurately determine pH values. The device consists of three parts: (1) an external reference (trifluoroacetic acid), (2) a temperature-sensing compound based on the chemical shifts of ethylene glycol or methanol, and (3) the pH micro-sensor compound NaF. Because pH micro-sensor compounds added to an aqueous solution have an influence on the pH, only a minimum amount of an NMR micro-sensor compound should be added to the sample. Quantitative NMR experiments in different setups (spherical NMR tubes, tubes with susceptibility plugs, Shigemi tubes) were conducted to determine the minimum amount of micro-sensor compound necessary for NMR measurements. A minimum number of 4.02 x 1016 nuclei was found to be sufficient for NMR signal observation using a 400-MHz spectrometer. The chemical shifts of pH-sensing NMR signals generally depend on temperature. Temperature-dependent NMR experiments were conducted to establish calibration curves through which the influence of temperature on the chemical shift can be corrected. The 19F signal of trifluoroacetic acid was found to have the least temperature-dependent chemical-shift variation and is suggested as independent standard for temperature-correction curve"--Abstract, page iii.

Advisor(s)

Woelk, Klaus

Committee Member(s)

Reddy, Prakash
Nam, Paul Ki-souk

Department(s)

Chemistry

Degree Name

M.S. in Chemistry

Publisher

Missouri University of Science and Technology

Publication Date

Summer 2017

Pagination

ix, 58 pages

Note about bibliography

Includes bibliographical references (pages 52-57).

Rights

© 2017 Ming Huang, All rights reserved.

Document Type

Thesis - Open Access

File Type

text

Language

English

Thesis Number

T 11484

Electronic OCLC #

1104294550

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