Coulomb Moisture Analyzer Principle Analysis and Its Advantages

Coulomb moisture analyzer is often used to determine the moisture content in gas. This method is simple, quick response, especially suitable for the determination of trace amounts of gas.

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Coulomb moisture analyzer working principle:

The Karl Fischer method for determining moisture is an electrochemical method. The principle is that the Cartesian reagent in the electrolysis cell of the instrument is in equilibrium when injected into a water-containing sample. Water participates in the redox reaction of iodine and sulfur dioxide in the presence of pyridine and methanol. Next, pyridine hydroiodide and pyridine methyl sulfate are generated, and the consumed iodine is generated at the anode by electrolysis, so that the redox reaction proceeds until the water is completely consumed.

According to Faraday’s law of electrolysis, the electrolysis of iodine is proportional to the amount of electricity consumed during electrolysis. The reaction is as follows:

H2OI2SO23C5H5N→2C5H5N·HIC5H5N·SO3

C5H5N·SO3CH3OH→C5H5N·HSO4CH3

In the electrolysis process, the electrode reactions are as follows:

Anode: 2I--2e→I2

Cathode: I22e→2I-2H2e→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 quantity of electrolytic iodine is equivalent to the quantity of electrolyzed water. The electrolysis of 1 mole of iodine requires 2*96,493 coulombs of electricity. The electrolysis of 1 millimole of water requires a quantity of electricity of 96,493 milli-coulombs of electricity. The moisture content of the sample is calculated according to equation (1): where: W—the moisture content in the sample, μg; Q --- electrolysis power, mC; 18 --- the molecular weight of water.

Coulomb Moisture Analyzer Applications:

A variety of organic and inorganic moisture determinations can be applied, but due to differences in the nature of the various compounds, the Cartesian Coulomb assay is an exclusive one only if there is no side reaction and no interference in the Carter-Kart reagent. Methods. The principle is (1) the side reaction can not produce water; (2) the sample can not consume iodine or release iodine.

Substances that mainly have side reactions and interference are classified into the following eight categories:

1. Salts, hydroxides, and oxides:

For example: Na2CO3HI→NaICO2H2OCa(OH)2H2SO4→CaSO4H2OMgOHI→MgI2H2 There are also some substances that can also cause side reactions such as: Ag2O, HgO, MnO2, PbO, PbO2 and ZnO

2. Both ketone and aldehyde compounds combine with methanol in the Carter's reagent to form ketals and acetals and release moisture.

This kind of material is not easy to measure with the Karlsson Coulometric Analyzer, but the Karl Fischer volumetric method can be used to determine the composition of the Carrageenan Reagent. For example, the replacement of methanol with ethylene glycol monomethyl ether or 2-methoxyethanol can achieve good results. It is worth noting that not all ketones and aldehydes can be measured by the Coulometric Coulomb method. For example, formaldehyde, trioxane, diisopropyl ketone, acetophenone, diphenyl ethanol Ketones and other substances will not react and release moisture when they enter the Carter's reagent. The accuracy of the Karl Fischer volumetric method can reach 10-4. For companies that produce ketones and aldehydes, as long as they meet the requirements, It is still recommended to use the Cartesian capacity method.

3, strong acid and acid will react with methanol in Carter's reagent to release water 2CH3OHH2SO4 → (CH3O) SO2H2OCH3OHHOOCH → CH3O-OCHH2O

4. The silanol/silicone terminal silanol group and the methanol in the Carter's reagent undergo a lipidation reaction to produce water. 5. The boron-containing compound boric acid and methanol undergo a lipidation reaction to generate water;

6, metal peroxide Carter reagent reaction generated water;

7. Substances that consume iodine react with iodine in the Carter's reagent, leading to high levels of moisture, such as iron salts, ketone salts, nitrites, thiosulfates, etc.