The method describes how to determine the oxygen content of water using an Orbisphere meter.
Water intended for use as an ingredient in the production of beer (brewing liquor) or other foods
Oxygen is present in water in varying concentrations. The oxygen content of cold tap water has a significant impact on iron pipes. If the water exhibits an oxygen deficiency (less than 2–3 mg/l O2), iron pitting can occur, since a protective layer between the water and pipe cannot form.
However, for boiler feed water, the absence of oxygen is normally required (depending upon the type of boiler, no more than 0.02–0.5 mg/l should be present) in order to prevent corrosion. The oxygen determination is vitally important (BOD5 value) for testing and evaluating wastewater.
An electrochemical cell consisting of two electrodes and electrolytes, and that is covered with a membrane permeable to oxygen, produces an electric current. The current is proportional to the permeability of the membrane to oxygen, i.e., proportional to the partial pressure of oxygen in the medium. Oxygen reacts at the cathode of the cell, which normally consists of a precious metal (e.g., gold), according to the following equation:
O2 + 2 H2O + 4 e- → 4 OH-
in which e- means one electron in the metal. The electron flux over the course of the reaction produces the current that is then measured. In addition, the temperature also has an impact on the amount of current, which can be compensated for electronically.