Definition
A trace dissolved oxygen meter is a specialized analytical instrument for the accurate determination of very low concentrations of dissolved oxygen in liquids. Its measurement range typically covers the microgram per liter level, making it suitable for processes and scientific research that are sensitive to oxygen content or require strict oxygen control. The instrument plays an important role in environmental monitoring, industrial process control, and laboratory analysis, providing continuous or intermittent dissolved oxygen data to help users assess redox status or biochemical activity.
Measurement principle
The measurement of trace dissolved oxygen meters is based on the principles of electrochemical or optical sensing. Electrochemical sensors usually use polar spectroscopy or galvanic cell methods, in which the working electrode and reference electrode are placed in an electrolyte and covered with a breathable membrane. Dissolved oxygen undergoes a reduction reaction on the electrode surface through the thin film, and the diffusion current generated is directly proportional to the partial pressure of oxygen, and the oxygen concentration can be calculated by measuring the current value. The optical sensor is based on the principle of fluorescence quenching, where specific sensitive substances fluoresce under excitation light, and their intensity and quenching time are affected by the surrounding oxygen molecules, and the oxygen content is indirectly measured by detecting changes in optical signals. Both principles enable micro-level measurements, and optical methods are becoming more popular due to their low consumption and low maintenance requirements.
Measurement method
The measurement methods of trace dissolved oxygen are mainly divided into online continuous monitoring and offline sampling measurement. Online monitoring immerses the sensor directly into the liquid to be measured for real-time data acquisition and recording, suitable for process control or long-term observation. For offline measurement, it is necessary to use a special sampling container to isolate the air, quickly transfer it to the instrument for analysis, and pay attention to avoiding contact between the sample and the atmosphere during operation. Calibration is a key step to ensure data accuracy, usually using a combination of zero point calibration and span calibration, zero point calibration uses oxygen-free solution, and span calibration is carried out according to saturated air or a standard solution with a specific oxygen concentration. During the measurement process, the temperature and pressure should be controlled, and the compensation calculation should be carried out according to the instrument requirements.
Influencing factors
Trace dissolved oxygen measurements are influenced by a variety of factors. Temperature changes change the solubility of oxygen and the response characteristics of the sensor, and most instruments have built-in temperature sensors for automatic compensation. The sample flow rate or agitation state affects the oxygen diffusion rate on the surface of the sensor membrane, and stable fluid conditions need to be maintained. Salinity or ionic strength may alter the activity coefficient of oxygen, and the calibration method should be selected according to the sample matrix. The integrity of the sensor membrane, electrolyte status, and electrode cleanliness can change over time, and regular maintenance and verification are necessary to ensure long-term stability. In addition, the presence of bubbles, reducing or oxidative interfering substances in the sample can also introduce measurement bias.
Applications
Micro dissolved oxygen meters are widely used in many industrial and scientific research fields. In the power industry, it is used to monitor trace oxygen in boiler feedwater and steam condensate to prevent corrosion and fouling. In the electronics industry, the preparation process of ultrapure water requires strict control of dissolved oxygen to ensure product quality. Food and beverage production focuses on the oxygen content of the filling process to extend shelf life. For environmental monitoring, it is used to assess hypoxic conditions in groundwater, deep aquifers of lakes or sediment interfaces. Aquaculture and research need to monitor the oxygen distribution of water bodies to ensure the living conditions of organisms. In addition, dissolved oxygen is one of the key parameters for reaction process control in the fields of chemical synthesis, biological fermentation, and materials science.
Instrument selection considerations
When choosing a trace dissolved oxygen meter, you should consider the measurement needs and environmental conditions. Clarify the measurement range and accuracy requirements to ensure that the instrument performance meets the application scenarios. Optical sensors are suitable for corrosive media such as hydrogen sulfide or for long-term continuous monitoring, and electrochemical sensors may respond better to rapid changes. Consider the instrument's ability to compensate for temperature and pressure, as well as whether it has an automatic calibration function. The on-site installation conditions determine the protection level of the instrument and the signal output method, and the online system must be compatible with the existing control network. Ease of maintenance, sensor life, and operating costs are also important considerations for long-term use. It is recommended to refer to relevant industry standards or methodological guidelines to ensure that the measurement data meets the specification requirements.