Galvanic oxygen electrodes for DO meters
The CellOx 325 Dissolved Oxygen (DO) electrodes are easy to use and maintain electrodes for taking DO field measurements. The DO electrodes are temperature compensated and waterproof to the IP 68 standard. The DO electrodes have a long working life of up to six months from one electrolyte refill. Plastic or steel armoring is available for the DO electrode to protect it from harsh field conditions. The DO electrodes can be easily cleaned with warm water for many applications and come with a vial of cleaning solution for the counter electrode.
What is Dissolved Oxygen (DO)?
Some oxygen is dissolved in practically every liquid. For example, at a temperature of 68 °F (20 °C) and an atmospheric pressure of 1013 mbar saturated water contains about 9 mg/l DO. Ethanol can contain up to 40 mg/l whereas glycerol only has about 2 mg/l.
Each liquid takes up oxygen until the partial pressure of oxygen in the liquid is in equilibrium with the air or gas phase in contact with it. The actual oxygen concentration depends on a number of factors, such as temperature, air pressure, oxygen consumption by microorganisms in a biodegradation process or oxygen production by algae, etc.
The DO concentration is important for the:
The determination of the DO concentration was formerly carried out by the WINKLER titration method. Today electrochemical measurement is a recognized method in numerous standard procedures.
In its simplest form a DO electrode contains a working electrode and a counterelectrode. Both dissolved oxygen electrodes are located in an electrolyte system which is separated from the sample by a gas-permeable membrane. The working DO electrode reduces the oxygen molecules to hydroxide ions. In this electrochemical reaction a current flows from the counterelectrode to the working DO electrode. The more DO present in the sample, the larger the current signal generated by the dissolved oxygen electrode. A meter connected to the DO electrode calculates the oxygen concentration in the sample from this signal.
Why Measure DO?
Dissolved oxygen (DO) is the amount of oxygen (O2) dissolved in water. DO measurements provide one of the best indicators of the health of a water ecosystem, as oxygen is a necessary element for all forms of life, including aquatic life. Oxygen enters water at the water surface through direct exchanges with the atmosphere. It is also produced as a byproduct of plant and phytoplankton photosynthesis. A decrease in DO levels is typically associated with an organic pollutant. DO is used by plants and animals for respiration, and by aerobic bacteria in the process of decomposition. When organic matter (such as animal waste or improperly treated wastewater) enters a body of water, algae growth increases. As the plant material dies off and decomposes, DO levels decrease. If the water at the surface is not mixed with deeper water layers, the water's DO levels can become stratified. DO levels can also vary according to the time of day, weather, and temperature. DO in water can range from 0-18 parts per million (ppm), but most natural water systems require 5-6 ppm to support a diverse population. As DO levels drop below 5.0 mg/L, aquatic life is put under stress. As DO levels decrease, pollution-intolerant organisms are replaced by pollution-tolerant worms and fly larvae. If DO levels fall below 1-2 mg/L for a few hours, large fish kills can result.