The effect of pressure upon the solubility of oxygen in water: Implications of the deviation from the ideal gas law upon measurements of fluorescence quenching

The effect of pressure upon the solubility of oxygen in water compressed up to 500 atmospheres (atm) was directly measured. Pressurized aqueous solutions were allowed to equilibrate with a low pressure atmosphere (air, total pressure, 1 atm; oxygen partial pressure, 0.2 atm) across a gas-permeable, pressure-resistant Teflon membrane, and the equilibrium molar concentration of oxygen determined chemically. The solubility of oxygen in water decreased exponentially with pressure up to approximately 200 atm. At higher pressures, decreases in the molar volume of oxygen in solution resulted in a slight deviation from this initial trend. Implications of these results upon measurements of fluorescence quenching by oxygen under conditions of elevated pressure, a probe for studying the structure of macromolecules, are discussed.