Definition
A laboratory dissolved oxygen meter is an analytical instrument used to measure the concentration of dissolved oxygen in liquids. Dissolved oxygen refers to oxygen dissolved in water or other liquids in a molecular state, and its concentration is one of the key parameters for evaluating the oxidation environment, biochemical processes and material conversion efficiency of liquids. The instrument is widely used in environmental monitoring, aquaculture, food and beverage, sewage treatment, and industrial process control.
Measurement principle
Laboratory dissolved oxygen meters are mainly based on electrochemical principles, and the common ones are polar spectroscopy (Clark electrode) and fluorescence quenching method. The polar spectroscopy method uses an electrode covering the breathable membrane, and the oxygen passes through the membrane to undergo a reduction reaction at the cathode, and the diffusion current generated is directly proportional to the partial pressure of oxygen, and the dissolved oxygen concentration is calculated by measuring the current value. When oxygen comes into contact with fluorescent substances, the fluorescence lifetime or intensity will be reduced due to the quenching effect, and the oxygen concentration is obtained by detecting changes in optical signals. Both principles have good selectivity and can be adapted to different measurement environments.
Measurement method
Laboratory dissolved oxygen measurement generally follows standard operating procedures. Instrument calibration is performed first, with common methods including zero point calibration (using an oxygen-free solution) and slope calibration (using air-saturated water or a standard solution with a known oxygen concentration). During measurement, the sensor is immersed in the solution to be tested, ensuring that the electrode membrane surface is clean and free of bubbles, and the results are recorded after the reading is stable. Some instruments support automatic temperature and salinity compensation, which can automatically correct output values based on input parameters or built-in sensors. After the measurement is completed, the electrode should be cleaned and stored according to the specifications.
Influencing factors
Dissolved oxygen measurements are influenced by a variety of factors. Temperature changes affect oxygen solubility and sensor response speed, often requiring real-time compensation. The liquid flow rate or agitation state can affect the oxygen diffusion balance on the membrane surface, and moderate flow can help to obtain stable readings. Changes in salinity or ionic strength can change oxygen activity, and salinity compensation is required for high-salt samples. In addition, aging, contamination or damage to the sensor membrane, as well as electrode electrolyte consumption, can lead to measurement deviations and require regular maintenance and verification.
Applications:
In environmental monitoring, the instrument is used to assess the self-purification capacity and ecological health of water bodies. The aquaculture field relies on dissolved oxygen data to regulate oxygen supply equipment to ensure biological growth needs. The food and beverage industry optimizes processes and product quality by monitoring the oxygen content of fermenters, filling lines, and other links. In industrial wastewater treatment, dissolved oxygen is a key control index of biochemical treatment units, which directly affects the treatment efficiency. In addition, in the field of scientific research and education, the instrument also provides basic data support for related chemical and biological process research.
Selection reference
When choosing a laboratory dissolved oxygen meter, it is necessary to comprehensively consider the measurement range, accuracy, response time and use environment. For routine water quality analysis, models with temperature compensation and basic calibration functions can meet the needs; If it is used for low oxygen or high salt samples, the lower detection limit and compensation algorithm of the instrument should be paid attention to. Portable designs are suitable for rapid on-site screening, while benchtop instruments are better suited for continuous or batch testing in the lab. In terms of sensor type selection, the electrode of the polar spectroscopy method needs to be replaced with the membrane and electrolyte regularly, while the fluorescence method is relatively easy to maintain but the initial investment is high. In addition, instrument data interfaces, protection levels and compliance (e.g., compliance with relevant national or international standards) should also be included in the assessment.