What is Karl Fischer titration?
Karl Fischer Karl Fischer method is one of the most accurate methods for measuring water in samples.
In this method, a water molecule reacts with an iodine molecule (I2) in the presence of SO2 and methanol solvent. Since the reaction is carried out in a stoichiometric ratio of 1:1, the water in the sample can be measured by measuring the consumption of iodine using an electrochemical method. Karl Fischer devices of Mettler Toledo are divided into two categories: volumetric and coulometric. Mettler Toledo Company offers you the best device for all types of samples and special applications.
Karl Fischer Volumetric
The Karl Fischer volumetric titration device by Mettler Toledo is suitable for measuring water content in the range of 0.001% to 100%. One advantage of the Karl Fischer volumetric system is that it allows direct introduction of solid or paste-like samples into the titration vessel. Using suitable organic solvents specific to the sample, the water content of the sample can be measured. Despite considerable advancements in producing Karl Fischer reagents, a stable titer for these reagents has not been achieved. As with all Karl Fischer devices worldwide, determining the titer factor for the Karl Fischer volumetric titrant must be performed continuously.
Karl Fischer coulometric
For measuring low amounts of water (from 10 µg to 100 mg of absolute water content), the coulometric method is ideal for determining water in liquids, solids, and gases.
Karl Fischer’s equation:
(RNH) SO4CH3 + 2 (RHN) I H2O + I2 + SO2 + CH3OH + 3 RN
Mettler Toledo Switzerland’s Karl Fischer instruments
Among the global manufacturers of these devices, Switzerland and the Mettler Toledo brand stand out as the oldest, most experienced, and the best. With over 80 years of expertise, exceptional precision, and the use of high-quality materials, Mettler Toledo distinguishes itself from other companies. The motto of major, long-term-focused companies is “Quality is the best advertisement.” For this reason, they have sustained their presence in global markets for many years.
One of the main concerns of laboratory device buyers due to the high purchase price is whether the device they choose will work for years without any problems. Will they receive the required technical and scientific services and support?
Fortunately, due to the existence of 30 years of sales of Mettler Toledo devices in Iran, by surveying the centers that use this company’s equipment such as scales, titrators, Karl Fischer, pH meters and conductivity meters, refractometers, density meters and spectrophotometers. It can be concluded that to what extent the customers of Mettler Toledo products have been satisfied. By spending high costs to train its technical staff abroad, this company also guarantees its after-sales service and does not leave its customers alone. Therefore, there are not few customers of this company who have been permanent and trusted us.
What is the difference between Karl Fischer volumetric titration and coulometric titration?
In the volumetric method, the titrant is added directly to the sample container, but in the coulometric method, the titrant is created electrochemically and simultaneously in the sample container. The coulometric method is generally used to measure and detect small amounts of water (less than 50-100 ppm).
When is tube with diaphragm and when is tube without diaphragm used?
C20 and C30 models of Mettler Toledo company are available with two types of tubes. One tube with diaphragm and one without diaphragm. For many applications we recommend tube without diaphragm. Because it does not need maintenance. For this reason, the unique design of this type of cells is also used to determine the amount of water in oils. Diaphragm tubes are recommended for measuring substances containing ketones. Or when the best accuracy is desired by the user.
When do we realize that we have to replace the molecular reservoir in the drying tube?
The most practical solution for this issue is to add some blue silica gel to the top of the suspect tube as an indicator. As soon as a pink color appears in the gel layer, it is time to replace the molecular sieve. Naturally, an increase in the drift time of the device can also indicate that the molecular sieve should be replaced.
How often do you need to change the solution in the titration container?
The first and clearest answer to this question is: as soon as the example is no longer solved. However, this is one of the reasons for changing the solution. The second reason is when the titrant contains iodine and the solvent contains other essential compounds for the Karl Fischer reaction. One of these compounds is sulfur dioxide, which can settle before the solvent’s solubility capacity is saturated. As a general rule, the solvent in systems containing these two compounds has an estimated capacity of 7 milligrams of water per liter of solvent. For example, in a titrant with a concentration of 5 mg/l, 280 mg of water requires 56 cc of the titrant.