China Education Equipment Purchasing Network News: Coulomb Moisture Analyzer is commonly used to determine the moisture content in the gas. This method is easy to operate, fast response, especially suitable for the determination of trace amounts in the gas.
In the biological shopping mall under the bio-worry-free network, a special column for coulometric moisture analyzers is set up, which contains a large number of detailed information on the performance, advantages, uses and quotations of well-known brands and related products. Suitable products.
Coulomb moisture analyzer working principle:
The Karl Fischer Coulometric method is an electrochemical method for measuring moisture.The principle is that the water sample is injected when the Karl Fischer reagent in the instrument's electrolytic cell reaches equilibrium, and water participates in the redox reaction of iodine and sulfur dioxide. Next, pyridine hydroiodide and pyridine methyl sulfate are generated, and the consumed iodine is produced by electrolysis at the anode, so that the oxidation-reduction reaction continues until the water is completely exhausted.
According to Faraday's law of electrolysis, the iodine produced by electrolysis is proportional to the amount of electricity consumed during electrolysis, and the reaction is as follows:
H2O I2 SO2 3C5H5N → 2C5H5N · HI C5H5N · SO3
C5H5N · SO3 CH3OH → C5H5N · HSO4CH3
During the electrolysis process, the electrode reaction is as follows:
Anode: 2I--2e → I2
Cathode: I2 2e → 2I-2H 2e → H2 ↑
It can be seen from the above reaction that 1 mole of iodine oxidizes 1 mole of sulfur dioxide, which requires 1 mole of water. So it is the equivalent reaction of 1 mole of iodine and 1 mole of water, that is, the amount of electrolytic iodine is equivalent to the amount of electrolytic water. The electrolysis of 1 mole of iodine requires 2 * 96493 coulombs of electricity, and the electrolysis of 1 millimole of water requires 96493 millicoulombs of electricity. The moisture content in the sample is calculated according to formula (1): where: W --- moisture content in the sample, μg; Q --- electrolytic power, mC; 18 --- molecular weight of water.
Application range of Coulomb Moisture Analyzer:
It can be applied to the determination of moisture in a variety of organic and inorganic substances, but due to the differences in the properties of various compounds, only when there is no side reaction and interference in the Karl Fischer reagent, the Karl Fischer Coulometric method is a special property. Method. The principle is that (1) side reactions cannot generate water; (2) samples cannot consume or release iodine.
There are eight types of substances that mainly have side reactions and interference:
1. Salt, hydroxide and oxide:
For example: Na2CO3 HI → NaI CO2 H2OCa (OH) 2 H2SO4 → CaSO4 H2OMgO HI → MgI2 H2 There are also some substances that will also cause side reactions, such as: Ag2O, HgO, MnO2, PbO, PbO2 and ZnO
2.The two types of compounds, ketone and aldehyde, will combine with the methanol in the Kas reagent to form ketals and acetals and release water.
Such substances are generally not easy to measure with a Karl Fischer Coulometer, but the Karl Fischer volumetric method can be used to change the composition of the Karl Fischer reagent, such as replacing methanol with ethylene glycol monomethyl ether or 2-methoxyethanol. The effect of the determination. It is worth noting that not all ketones and aldehydes can be measured by the Karl Coulomb method. For example, formaldehyde, triacetaldehyde, diisopropyl ketone, acetophenone, diphenylethanol Ketones and other substances will not react and release water when they enter the Kjeldahl reagent. In view of the measurement accuracy of the Kjeldahl volumetric method, which can reach 10-4, from the production of ketones and aldehydes, as long as the requirements for use are met, It is still recommended to use the Karl Fischer volume method.
3. The strong acid will react with the methanol in the Karl Fischer reagent to release water 2CH3OH H2SO4 → (CH3O) SO2 H2OCH3OH HOOCH → CH3O-OCH H2O
4. The silanol group at the silanol / siloxane terminal and the methanol in the Kaschen reagent undergo lipidation to generate water. 5. The boron-containing compound boric acid and methanol undergo lipidation to generate water;
6. The reaction of metal peroxide and Karl Fischer reagent generates water;
7. Substances that consume iodine will react with the iodine in the Kaplan reagent, resulting in high moisture content, such as iron salt, ketone salt, nitrite, thiosulfate, etc.
The following are the product pictures and models of 4 Coulomb Moisture Analyzers, for reference only:
SF-3B Trace Moisture Analyzer
SF-3 Trace Moisture Analyzer
WS-2 Trace Moisture Analyzer
SF-1 Trace Moisture Analyzer
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