Air calibration

high-resolution terminology - matching measurements at high-resolution

Air calibration

Description

Air calibration of an oxygen sensor (polarographic oxygen sensor) is performed routinely on any day before starting a respirometric experiment. The volume fraction of oxygen in dry air is constant. An aqueous solution in equilibrium with air has the same partial pressure as that in water vapour saturated air. The water vapour is a function of temperature only. The partial oxygen pressure in aqueous solution in equilibrium with air is, therefore, a function of total barometric pressure and temperature. Bubbling an aqueous solution with air generates deviations from barometric pressure within small gas bubbles and is, therefore, not recommended. To equilibrate an aqueous solution ata known partial pressure of oxygen [kPa], the aqueous solution is stirred rigorously in a chamber enclosing air at constant temperature. The concentration of oxygen, c_O2 [µM], is obtained at any partial pressure by multiplying the partial pressure by the oxygen solubility, S_O2 [µM/kPa]. S_O2 is a function of temperature and composition of the salt solution, and is thus a function of the experimental medium. The solubility factor of the medium, F_M, expresses the oxygen solubility relative to pure water at any experimental temperature. F_M is 0.89 in serum (37 °C) and 0.92 in MiR06 or MiR05 (30 °C and 37 °C).