Definition
A laboratory dissolved oxygen meter is an analytical instrument used to accurately determine the concentration of dissolved oxygen in liquids. Dissolved oxygen refers to oxygen dissolved in water or other liquids in a molecular state, and its content is usually expressed as mass concentration or saturation. This instrument plays an important role in environmental monitoring, aquaculture, food and beverage, sewage treatment, and industrial process control, and is one of the key tools for evaluating the ecological health and chemical reaction conditions of water bodies.
Principle
Laboratory dissolved oxygen meter measurements are mainly based on electrochemical or optical sensing principles. Electrochemical sensors typically feature a Clark electrode, which consists of a cathode, anode, and electrolyte, covered with an oxygen-permeable membrane. Oxygen undergoes a reduction reaction at the cathode through the thin film, generating a diffusion current directly proportional to the oxygen concentration, and the dissolved oxygen concentration can be calculated by measuring the current value. The optical sensor is based on the principle of fluorescence quenching, and the intensity and quenching time of specific fluorescent substances fluoresce under the irradiation of excitation light, and their intensity and quenching time are affected by the oxygen molecules in the environment, and the oxygen content is indirectly determined by detecting changes in optical signals.
Measurement method
Laboratory dissolved oxygen measurements generally follow standardized operating procedures. Calibration is required before use, and common calibration points include zero-oxygen and saturated oxygen environments. During measurement, the sensor is immersed in the liquid to ensure that there are no air bubbles on the surface of the probe, and the result is recorded after the reading is stable. Some instruments support automatic temperature and salinity compensation to improve measurement accuracy. For special samples, anti-interference measures may be required, such as avoiding strong agitation or adding chemical protective agents.
Influencing factors
Dissolved oxygen measurements are influenced by a variety of factors. Temperature changes change oxygen solubility and sensor response characteristics, often requiring simultaneous monitoring and compensation. Liquid salinity affects the rate of oxygen diffusion, and high-salt samples need to be selected with special sensors or corrected. Changes in atmospheric pressure will change the partial pressure of oxygen, and pressure correction should be paid attention to when measuring in plateau areas. The liquid flow state can affect oxygen exchange on the membrane surface, and moderate agitation can help maintain measurement consistency. In addition, chemicals such as hydrogen sulfide or chlorine can interfere with electrode reactions, so anti-interference sensors should be selected based on the nature of the sample.
Application:
In the field of environmental monitoring, dissolved oxygen meters are used to assess the water quality of rivers, lakes and oceans, reflecting the self-purification capacity and ecological balance of water bodies. In aquaculture, dissolved oxygen monitoring helps optimize the oxygen supply system and ensure the living environment of farmed organisms. The food and beverage industry extends product shelf life and maintains flavor stability by controlling dissolved oxygen. In the process of industrial wastewater treatment, dissolved oxygen data is used to regulate the aeration system and improve the efficiency of biochemical treatment. In addition, dissolved oxygen is also an important process control parameter in industrial processes such as biological fermentation and boiler water supply in the power industry.
Selection
When choosing a laboratory dissolved oxygen meter, it is necessary to comprehensively consider the measurement range and accuracy requirements, which usually cover 0 to 20 milligrams per liter and the accuracy can reach ±0.1 milligrams per liter. Optical sensors are suitable for contamination or low maintenance, while electrochemical sensors have a wide range of applications. The instrument should have automatic temperature compensation and salinity correction functions. The operation interface should be clear and intuitive, and the data storage and output functions should meet the requirements of laboratory records. In addition, sensor replacement convenience and maintenance costs should also be taken into account.