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Studies on dissolved molecular oxygen in pure and sea water Mirhej, Michael Edward

Abstract

Dissolved oxygen was studied in distilled water and salt solutions by means of nuclear magnetic resonance. The free induction technique was employed to measure the spin lattice relaxation time, T-^, for oxygen-free distilled water and for water containing oxygen under one atmosphere of air and one atmosphere of oxygen at temperatures of 1° to 75°C. The same measurements were made for solutions of 0.5 M sodium chloride at temperatures of 1° to 40°C. The spin lattice relaxation probability, 1/T[subscript 1(c)], in the presence of paramagnetic oxygen, was attributed to two relaxation mechanisms: the first a dipole-dipole interaction and the second a hyperfine interaction. The two terms were evaluated from measurements of T[subscript 1(c)] at two different magnetic field strengths at 20°C. Using the theoretical relationship between the dipole-dipole term and η/T, the results were used to evaluate the hyperfine term at different temperatures. The activation energy obtained from the variation of the dipole-dipole term with temperature was assumed to represent the energy required to break one hydrogen bond between two water molecules. The activation energy found for the hyperfine term was taken as a measure of the breaking of a hydrogen bond between one oxygen molecule and an aggregate of water molecules. The activation energy of the hyperfine term was found to be a function of temperature. Comparison of this quantity with heats of solution of dissolved oxygen in distilled water and salt solution showed a similar pattern of change in both. Oxygen supersaturation was studied in sea water cultures of Nitzschia closterium and Chlorella strain "A" at a temperature of 12°C. Saturation values up to 200% were reached under illumination with light energy of 9.2x10[power -3] langlies/min. Nitzschia was found to be more photosynthetically active, under the same culture conditions, than Chlorella. Oxygen production by Nitzschia was shown to be a function of the difference in photosynthetic pigment concentrations (chlorophyll-a — non-astacin carotenoid), total alkalinity, and the change in catalytic activity of the medium. Variation of oxygen concentration in Nitzschia cultures under light and dark periods indicated a mechanism by which oxygen may escape as microbubbles to the atmosphere. The rate of oxygen desupersaturation was measured in water free of organisms. The rate increased with increase of ion content and with the surface to volume ratio of the water column, but was not influenced by addition of siliceous particulate matter to the supersaturated water. Small addition of a surface active agent (heptanoic acid) increased the oxygen desupersaturation rate but further addition decreased the rate.

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