This International Standard specifies an electrochemical method for the determination of dissolved oxygen in water by means of an electrochemical cell which is isolated from the sample by a gas permeable membrane.
Depending on the type of probe employed, meas-urement can be made either as concentration of oxygen in milligrams per litre, percentage saturation {% dissolved oxygen) or both. The method meas-ures oxygen in water corresponding to 0 % to 100 % saturation. However, most instruments per-mit measurement of values higher than 100 % i.e. supersaturation.
The method is suitable for measurements made in the field and for continuous monitoring of dissolved oxygen as well as measurements made in the labo-ratory. It is the preferred method for highly coloured and turbid waters, and also for waters containing iron and iodine fixing substances, all of which may interfere in the iodometric method specified in ISO 5813. Gases and vapours such as chlorine, sul-fur dioxide, hydrogen sulfide, amines, ammonia, carbon dioxide, bromine and iodine which diffuse through the membrane, may interfere, if present, by affecting the measured current. Other substances present in the sample may interfere with the meas-ured current by causing obstruction, or deterioration of the membrane or corrosion of the electrodes. These include solvents, oils, sulfides, carbonates and algae.
The method is suitable for natural, waste and saline waters. If used for saline waters such as sea waters, or estuarine waters, a correction for salinity is es-sential.