[en] A preferred test system comprises a chemical and/or biological sample in a liquid test medium and contains both a liquid and a gas phase that simulates air-water gas exchanges. It operates intermittently, with additions and eliminations of liquids being decoupled in time so that to make sure the medium is well mixed before eliminating any liquid; requirement for expensive fixed flow pumps, or accurate flow meters are eliminated while accurate measurements of fluxes between the chemical and/or biological sample, the liquid and the gas phase are possible by mass balance between added and eliminated liquids.
