Both the coulometric moisture analyzer and the volumetric moisture analyzer are Karl Fischer moisture analyzers; it is the method of measuring moisture proposed by Karl Fischer in 1935. Below we explain in detail the difference between Coulomb method and volumetric moisture analyzer. Karl Fischer moisture analyzer
The volumetric Karl Fischer moisture analyzer accurately titrates Karl Fischer reagent into a sealed titration cell added to the tested sample through a precision metering system, and calculates the total amount of Karl Fischer reagent consumed when reaching the end point. The total amount of water in the sample that is reacted, and then the water content in the sample.
advantage:
1. Accurate judgment of the reaction end point, which can accurately detect the moisture content in various liquid, solid and some gas samples;
2. As long as there is a suitable total amount of water in the titration cell, the water in the sample can be measured quickly and accurately;
3. The time of moisture determination is shorter than that of the heating method rapid moisture analyzer, and the average is from tens of seconds to several minutes;
4. For some poorly soluble, insoluble substances, and other volatile substances that are not suitable for heating method detection, auxiliary equipment, such as cassette headspace sampler (cassette furnace), etc. can be used for accurate detection;
Disadvantages:
1. The detection accuracy is related to many factors of the instrument, and it has high requirements for the design and manufacture of the instrument;
2. Auxiliary equipment and toxic Karl Fischer reagent are needed in the detection process; it is easy to cause environmental pollution;
The operation mode of the coulometric Karl Fischer moisture analyzer is compared with that of the volumetric method. The user puts the Karl Fischer reagent (divided into catholyte and anolyte) into the closed coulometric titration cell beforehand. The sample to be tested is added to the Karl Fischer reagent environment of the sealed titration cell, and the total amount of water that is reacted is calculated by calculating the amount of electrolytic iodine consumed after the water in the titration cell is completely reacted by the iodine produced by electrolysis. , Because the unit of electricity is Coulomb, it is called Coulomb Moisture Meter, and it can also be called Coulomb Moisture Meter.
advantage:
1) The Coulometric Karl Fischer moisture analyzer detects the moisture content by calculating the electricity produced by the anode electrolysis of iodine. Under the condition of reliable instrument quality, the moisture content can be measured very accurately.
2) When detecting trace amounts of water, the electrolysis speed can meet the requirements, and it is often possible to detect a sample in ten to tens of seconds, and the detection efficiency is extremely high;
3) Compared with the volumetric Karl Fischer moisture analyzer, the coulometric Karl Fischer moisture analyzer does not require a precise titration system, no transmission structure and a high-precision measurement system, and the possible instrument failures are greatly reduced;
Disadvantages:
1) Since the coulometric method measures moisture by calculating the amount of electricity produced by electrolytic iodine, it must be ensured that the sample to be tested does not have the following side reactions:
A. React with Karl Fischer reagent to produce water;
B. The sample cannot consume iodine or react to release iodine in the detection cell; affected by this: some samples such as iron salts, nitrites, ketone salts, oxides, hydroxides, aldehydes, ketones, metal peroxides, Strong oxidants, strong acids, boron-containing compounds, etc. cannot be detected by coulometric method;
2) Because the electrolysis speed of iodine in the electrolytic cell is very slow, if the water content in the sample is high, the electrolysis speed cannot keep up with the reaction speed of the water, which will cause the detection efficiency to be greatly reduced, the electrolysis time is long, and the working life of the instrument is shortened , And if the detection is done by reducing the amount of sample, the reliability of the sample results will be reduced. Therefore, the Coulometric Karl Fischer Moisture Analyzer is recommended to be used for the detection of moisture content below 1000PPM.