Controlling O2 and CO2 level
Contents
Reasons to control O2 and CO2 level
Cells need oxygen for their respiration and CO2 to have the correct pH and carbonate concentration. The pH and carbonate concentration can be controlled by "CO2-independent media" that are media with buffers, i.e. mainly carbonate salts that are balanced to keep the concentrations and pH correct. Over time, however, it is better for the media with cells to be in equilibrium with air with the correct concentration of O2 and CO2.
Ways of achieving correct gas mixtures
There are two basic ways of controlling the gas mixture composition: flow control or pressure-volume control
Flow control
Commercial gas blender measure the flow of each gas and regulate the flow of each input gas to achieve a controlled composition of the output gas. This requires a constant overall flowrate and no changes in the pressure at the outlet of the device. These gas blenders are therefore well suited to control the gases in volumes that are at atmospheric pressure and in contact with the media (in order to establish diffusive equilibrium) where the cells are.
Pressure - volume control
If we have a container with a manometer (pressure sensor + display), accurate valves and pressurized pure gases we can let in the gases successively to control the final composition. First let's assume that the gases are ideal
and that the gas mixtures are ideal as well
If we desire a CO2 concentration of
Equation