Karl moisture meter
Karl moisture meter

Karl moisture analyzer / Karl Fischer moisture analyzer Karl Fischer moisture determination, has many international standards, such as ISO, ASTM, DIN, BS, and JIS recognized as the highest accuracy of the method.

Applicable to the determination of various substances moisture content. Is the most trusted moisture analysis and measurement equipment. Wide range of applications for solid, liquid and gas samples. If the solid sample can not be directly measured, it can be connected to the moisture vaporization device for measurement. When combined with the moisture vaporization device, automatically move the sample tray, set the gasification temperature, set the carrier gas ventilation time and other measurement conditions, can be controlled by the host and automatic measurement. Good reproducibility, high accuracy, time-saving and convenient.


Karl Fischer method proposed by Karl Fischer since 1935, the use of I2, SO2, pyridine, anhydrous CH3OH (water content below 0.05%) formulated as reagents, measured water equivalent of reagents in the reagent and the water in the sample After the reaction, by calculating the consumption of reagents to calculate the water content of the sample, the International Organization for Standardization as a measure of international standards for trace moisture, our country also put this method as a national standard measure trace moisture.


In the presence of water, the water in the sample reacts with SO2 and I2 in the Karl Fischer reagent to produce a redox reaction.
I2 + SO2 + 2H2O → 2HI + H2SO4
However, this reaction is a reversible reaction, when the concentration of sulfuric acid reaches 0.05% or more, that can reverse reaction. If we allow the reaction to proceed in a positive direction, we need to add a suitable alkaline material to neutralize the acid generated during the reaction. Experiments show that adding pyridine in the system, so that the reaction can be carried out to the right.
3 C5H5N + H2O + I2 + SO2 → 2 hydroiodide pyridine + sulfuric anhydride pyridine
Pyridine generated sulfuric anhydride instability, can react with water, consume part of the water and interfere with the determination, in order to make it stable, we can add anhydrous methanol.
Sulfuric acid anhydride pyridine + CH3OH (anhydrous) → pyridine methylsulfate
We write the above three-step reaction as the general reaction:
I2 + SO2 + H2O + 3 Pyridine + CH3OH → 2 Hydrogen iodate + Pyridine methylsulfate
It can be seen from the reaction formula 1mol water needs 1mol iodine, 1mol sulfur dioxide and 3mol pyridine and 1mol methanol to produce 2mol pyridine hydroiodide, 1mol pyridine methyl sulfates. This is the theoretical data, but in fact, the amount of SO2, pyridine, CH3OH are excessive, after the completion of the reaction, the excess of free iodine showed reddish brown, you can determine the end point.
I2: SO2: C5H5N = 1: 3︰10
2, Karl Fischer reagent preparation and calibration
If methanol as solvent, reagent I2, SO2, C5H5N (water content below 0.05%) the proportion of the three molecules is: I2: SO2: C5H5N = 1 ︰ 3︰10
The effective concentration of this reagent depends on the concentration of iodine. The reason why the effective concentration of the newly prepared reagent is continuously decreased is that each component of the reagent also contains some water itself. However, the main reason for the decrease of the reagent concentration is that it is caused by some side reactions and consumes a relatively high amount of iodine.
This also shows that the preparation of this reagent to be equipped with separate, points A and B two reagents and were stored, Pro then mixed, and to be calibrated. However, the Karl Fischer moisture measuring reagent used on the market of our country, whether it is one-component or two-component, is generally prepared by the manufacturer and can be directly used. However, since Karl Fischer reagent is a very poor Stable mixed material, so the user must be calibrated in use to determine its true water equivalent data.
Karl Fischer measure moisture, you need to pay attention to the following points:
① This method applies to most organic samples, including food samples of candy, chocolate, fat, lactose and dehydrated fruits and vegetables;
② strong reductive material in the sample, including the sample of vitamin C can not be determined; samples containing ketones, aldehydes, ketal and acetal reaction occurs, you must use a dedicated test of aldehyde and ketone reagents. For some samples that do not dissolve in methanol, look for another suitable solvent for dissolution testing, or use a Karl Fischer oven to evaporate water and determine.
③ Karl Fischer method can not only measure the free water in the sample, but also measure the bound water, that is, the result measured by this method reflects the total moisture content in the sample more objectively.
④ solid sample fineness of 40 mesh is appropriate, it is best to use the grinder instead of grinding to prevent moisture loss.

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