Generally, the trace moisture analyzer we use adopts the detection principle of the Karl Fischer coulometric titration method. The Karl Fischer method is referred to as the Fischer method, which is a volumetric separation method for determining moisture. The following is a detailed introduction.
1. The Fischer method is an iodometric method. Its basic principle is that when using iodine to oxidize sulfur dioxide, a certain amount of water is required to participate in the reaction: I2SO22H2O-2HIH2SO4. This reaction is reversible. Adding pyridine to the system can make the reaction toward Go right. In the process of determination, pyridine is a better reagent, and pyridine can also combine with iodine and sulfur dioxide to reduce the vapor pressure of the two. Therefore, the reagent needs to be added to methanol or another solvent containing active OH groups.
2. The Karl Fischer moisture determination method is a method of measuring the moisture content of a sample with methanol as the medium and Karl Fischer's solution as the titrant. This method is simple to operate and highly accurate, and is widely used in petroleum, chemical, pesticide, dye, food and other fields. It is especially suitable for samples that are easily destroyed by heat. Not only can free water be measured, but also bound water can be measured. It is often used as a standard analysis method for moisture, especially trace moisture. But it is not suitable for samples containing strong reducing substances such as VC.
3. Karl Fischer reagent is a reagent used to determine trace moisture in certain substances. Its components are: methanol, pyridine, iodine, and sulfur dioxide. There are two methods for determining the end point: the visual method and the potentiometric method.
The main components are I2, SO2, C5H5N, CH3OH. The basic principle of the Karl Fischer method is that when I2 oxidizes SO2, a quantitative amount of H2OI2SO22H2O=2HIH2SO4 is required. This reaction is a reversible reaction. To make the reaction proceed forward, it is necessary to add an appropriate alkaline substance And the acid produced by the reaction, pyridine (C5H5N) can meet this requirement, adding methanol can avoid side reactions. The Karl Fischer reagent is brown because it contains iodine. When I2, SO2, and H2O react, the iodine brown color fades away, and this method uses the brown color as the titration end point.
4. The Karl Fischer method is a non-aqueous titration method, and all containers must be dried. If 1L of Karl Fischer reagent is mixed with 6g of water during preparation and storage, the reagent will become invalid. Karl Fischer reagent is a reagent for determining trace moisture in organic matter, so it is also called water reagent, also known as Karl Fischer reagent.
