What are the different types of analytical moisture analyzers?
Classical moisture analysis methods have been gradually replaced by various moisture analysis methods. At present, there are mainly five types of moisture analyzers in the market. Moisture analysis methods can generally be divided into two categories, namely physical analysis and chemical analysis.
1. Karl Fischer Moisture Analyzer: Karl Fischer method referred to as Fischer method, is a capacity split method for measuring moisture proposed by Karl Fischer in 1935. The Fischer method is the most specific and accurate method for water among various chemical methods for determining the moisture content of substances. Although it is a classic method, it has been improved in recent years to improve accuracy and expand the measurement range. It has been listed as a standard method for moisture determination in many substances. The Fischer method is an iodometric method, and its basic principle is that when using iodine to oxidize sulfur dioxide, a certain amount of water is required to participate in the reaction: 12+S02+2H2O=2HI+H2SO4 The above reactions are reversible. In order to make the reaction move in the positive direction and proceed quantitatively, an alkaline substance must be added. Experiments have proved that pyridine is the most suitable reagent, and pyridine can also combine with iodine and sulfur dioxide to reduce the vapor pressure of both. Therefore, the reagent must be added to methanol or another solvent containing active OH groups to convert pyridine sulfate anhydride into stable pyridine methyl hydrogensulfate.
2. Infrared moisture meter: Infrared heating mechanism: When far infrared rays radiate to an object, absorption, reflection and transmission can occur. However, not all molecules can absorb far-infrared rays, only those polar molecules that show electricity can work. Water, organic substances and high molecular substances have a strong ability to absorb far infrared rays. When these substances absorb far-infrared radiation energy and make their molecular and atomic vibration and rotation frequency consistent with the frequency of far-infrared radiation, it is very easy for molecules and atoms to resonate or rotate, resulting in greatly increased motion, which is converted into The heat can raise the internal temperature, so that the material can be softened or dried quickly.
3. Dew point moisture meter: The dew point moisture meter is easy to operate, the instrument is not complicated, and the measured results are generally satisfactory. It is often used for the determination of trace moisture in irritating gases. However, this method has a lot of interference, and some easy-to-cool gases, especially when the concentration is high, will condense before water vapor and cause interference.
4. Microwave moisture meter: Microwave moisture meter uses microwave field to dry samples, which accelerates the drying process. It has the characteristics of short measurement time, convenient operation, high accuracy and wide application range. It is suitable for grain, paper, wood, textile and chemical industry. The moisture determination in granular, powdery and viscous solid samples such as products can also be applied to the determination of moisture in petroleum, kerosene and other liquid samples.
5. Coulometric moisture meter: Coulomb moisture meter is commonly used to measure the moisture contained in the gas. This method is easy to operate and responds quickly, and is especially suitable for the determination of trace moisture in gas. If it is determined by general chemical methods, it is very difficult. However, the electrolysis method is not suitable for the determination of alkaline substances or conjugated dienes.
