O2 solubility in aqueous media determined by a kinetic method.

Area of Science:

• Analytical Chemistry
• Biochemistry
• Physical Chemistry

Background:

• Accurate determination of oxygen (O2) solubility is crucial for understanding various chemical and biological processes.
• Existing methods for O2 solubility measurement can be imprecise, particularly in complex solutions or over a range of temperatures.
• The reaction between NADH (nicotinamide adenine dinucleotide) and O2, catalyzed by NADH oxidase, provides a basis for kinetic analysis.

Purpose of the Study:

• To develop and describe a precise kinetic method for determining O2 solubility in diverse aqueous solutions.
• To establish the molar stoichiometry between hydrogen ion (H+) and O2 uptake in the NADH oxidation reaction.
• To provide data on O2 solubility in common solutions (water, KCl, sucrose) at various temperatures.

Main Methods:

• A kinetic approach utilizing response-matched electrodes to measure the rates of H+ and O2 uptake.
• The core reaction is NADH + H+ + 1/2O2 → NAD+ + H2O, catalyzed by NADH oxidase.
• H+ electrode calibration against standard HCl; O2 solubility calculated from recorded uptake rates in an anaerobic system with excess NADH.

Main Results:

• Demonstrated precise molar stoichiometry between H+ and O2 uptake when NADH is in excess.
• Reported O2 solubility values at 25°C and 760 mm Hg for distilled H2O (516 nmol O/ml), 0.15 M KCl (480 nmol O/ml), and 0.25 M sucrose (458 nmol O/ml).
• Provided data and equations for O2 solubility in buffered KCl and sucrose solutions from 5°C to 40°C.

Conclusions:

• The described kinetic method offers accurate and precise determination of O2 solubility in solutions of varying composition and temperature.
• The method's reliability stems from the linear and stoichiometric relationship observed under specific reaction conditions (excess NADH).
• Identified limitations of previous methods, such as gradual endpoints and overestimation of O2 solubility when O2 is in excess.