Definition
The Coulomb moisture meter is an electrochemical principle-based instrument used to determine the content of trace amounts of moisture in a substance. This method directly calculates the moisture mass in the sample by measuring the amount of electricity required for electrolysis of water, which is a kind of absolute measurement method. Its measurement range is usually suitable for low-moisture samples and has clear application value in quality control and process monitoring in many industrial and scientific fields.
Principle
The core principle of the Coulomb water meter is Faraday's law of electrolysis. The instrument contains an electrolytic cell filled with water-absorbing reagents (e.g., iodine-containing Karl Fischer reagent). When the sample is introduced, the moisture reacts quantitatively with the reagent. An electric current is applied to the electrolytic electrode to regenerate the iodine consumed in the reaction until the water is completely reactive. According to Faraday's law, the amount of electricity required to produce iodine by electrolysis is directly proportional to the water mass. The calculation formula is as follows:
m = (Q × M) / (F × z)
where m represents the water mass, Q is the total amount of electricity consumed during the electrolysis process, M is the molar mass of water, F is the Faraday constant, and z is the number of electron transfers corresponding to each molecule of water electrolysis. By accurately measuring the charge Q, the moisture content in the sample can be directly calculated.
Measurement method
The measurement process typically involves the following steps: The cell is first pre-electrolyzed to bring the reagent to an aqueous state. The accurately weighed sample is then introduced into the electrolytic cell, where the moisture in the sample reacts with the reagent. The instrument automatically starts the electrolysis, and monitors the electrolysis current and time in real time, and integrates to obtain the total power. Finally, according to the quantitative relationship between electricity and water quality, the moisture content results are directly displayed. The entire measurement process is automatically controlled by the instrument, and the operator is mainly responsible for sample preparation and injection.
Influencing factors
The accuracy of the measurement results is influenced by several factors. Sample properties are one of the key factors, and some components in the sample may react with reagents and interfere with moisture determination. Insufficient environmental humidity control may lead to external moisture intrusion, affecting the background and measurement stability. The state of the electrolytic cell also needs to be paid attention to, as the decrease in reagent efficiency or electrode contamination may reduce the reaction efficiency and electrolytic current response. In addition, the uniformity and representativeness of the sample injection, as well as the accuracy of the instrument circuit's measurement of weak currents, play a role in the final result.
Application:
This instrument is widely used in fields where accurate determination of trace amounts of moisture is required. In the petrochemical industry, it is used to monitor the moisture content in oils, solvents and gases. In the power industry, it is used for moisture analysis of insulating media such as insulating oils and sulfur hexafluoride. In the food industry, it can be used to control the moisture of some raw materials and finished products. In the field of polymer and materials science, it is used for moisture determination of plastic particles, resins and powdered materials. In addition, it is also used as a routine analytical tool for substance purity identification and process research in the analytical laboratories of scientific research institutions.
Selection
When choosing a coulomb moisture meter, multiple technical parameters need to be considered. The measurement range and sensitivity should match the expected moisture content of the sample to be tested. The sample type determines the choice of injection method, such as injection injection, Kardashian oven injection, or gas carrier gas injection. The electrolysis speed and automatic control of the instrument affect the analysis efficiency. Data management and compliance functions, such as audit trails and data exports, are valued in some regulated laboratories. The long-term operating stability of the instrument, the cost of reagent consumption, and the technical support and service network provided by the manufacturer are also aspects that need to be evaluated in actual selection.