The classification of moisture analyzers, what is the difference between different classifications
What types of moisture analyzers are there? There are many commercially available moisture analyzers, which are divided into the following types according to the test methods:
Infrared method instrument: It is characterized by small size, wide measurement range and poor accuracy. It is suitable for the determination of wood, paper and other materials with a moisture content of 5%-90%. It has a simple structure and low price.
Karl Fischer coulometric instrument: its main principle is to calculate the change of electrical conductivity after a chemical reaction. It has a complex structure, a large volume, and a relatively high degree of determination. It is suitable for the determination of moisture content below 100PPm. It is generally used for the determination of products in chemical, pharmaceutical and other industries that have very strict requirements on moisture such as anionic polymerization, or for large-scale color printing factories with multiple frequencies, and the price is relatively expensive.
Karl Fischer volumetric method: Its structure is relatively simple, its volume and density are moderate, and it is suitable for the determination of moisture content of 10PPm-10%. It is generally used for the determination of products in chemical, pharmaceutical and packaging industries that have strict requirements on moisture. The price ranges from several thousand yuan. ranging from tens of thousands of dollars. For the general flexible packaging industry, when measuring the moisture content of ethyl acetate and other solvents, the Karl Fischer volumetric moisture analyzer can fully meet the requirements of 2-10 times of determination per day, and the economy is relatively good.
What is the difference between the Karl Fischer volumetric method and the Karl Fischer coulometric method?
Karl Fischer Volumetric Moisture Determination Principle When Karl Fischer volumetric method measures moisture content, it is mainly based on the electrochemical reaction: I2+2eó2I- When I2 and I- exist in the solution of the reaction cell, the reaction occurs at the positive and negative sides of the electrode. Both ends are carried out simultaneously, that is, I2 is reduced on one electrode, and I- is oxidized on the other electrode, so a current flows between the two electrodes. If there is only I- but no I2 in the solution, no current will flow between the two electrodes. The Karl Fischer reagent contains active ingredients such as pyridine and iodine. When it is metered and dropped into the reaction cell, it can react with the water in the solution to be tested as follows: H2O+SO2+I2+3C5H 5N→2C5H5N·HI+C5 H5N·SO3 C5H5N·SO3+CH3 OH →C5H5N•HSO4CH3 C5H5N•HI→C5H5N•H++ I- This reaction continues to consume water and generate I-, until the end of the reaction titration, the water is consumed. At this time, the solution has a small amount of Karl Fischer reagent that has not reacted, so that I2 and I- exist simultaneously. The solution between the two platinum electrodes begins to conduct electricity, and the end point is indicated by the current, and the titration is stopped. The water content in the solution is thus calibrated by metering the consumed Karl Fischer reagent volume (capacity).
