Moisture determinationIt can be control analysis of industrial production or quality inspection of industrial and agricultural products; Moisture can be determined from products measured in tons or analyzed in the laboratory using only a few microliters of the test solution; It can be a constant moisture analysis with a moisture content of several percent to tens of percent, or a trace moisture analysis with a moisture content of less than one millionth, and so on.
Moisture analysis methods can generally be divided into two categories, namely physical analysis and chemical analysis. The classic moisture analysis method has gradually been replaced by various moisture analysis methods. Currently, there are mainly five types of moisture measuring instruments on the market
1. Karl Fischer moisture analyzer:
The Karl Fischer method, abbreviated as the Fischer method, is a volumetric separation method proposed by Karl Fischer in 1935 for determining moisture content. The Fei Xiu method is the most specific and accurate method 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 enhance accuracy and expand measurement range, and has been listed as a standard method for determining moisture in many substances.
The basic principle of the Fexiu method for iodometry is to use iodine to oxidize sulfur dioxide, which requires a quantitative amount of water to participate in the reaction:
12十S02十2H2Ｏ=2HI十H2SO4
The above reaction is reversible. In order to move the reaction in the positive direction and proceed quantitatively, alkaline substances must be added. Experimental results have shown that pyridine is the most suitable reagent, and it also has the ability to bind with iodine and sulfur dioxide to reduce their vapor pressures. Therefore, the reagent must be added to methanol or another solvent containing active OH groups to convert sulfur-containing pyridine into stable methyl hydropyridine sulfate.
2. Infrared moisture analyzer:
Infrared heating mechanism: When far-infrared radiation reaches an object, it can undergo absorption, reflection, and transmission. However, not all molecules can absorb far-infrared radiation, only polar molecules that exhibit electricity can be affected. Water, organic matter, and polymer substances have strong absorption properties for far-infrared radiation. When these substances absorb far-infrared radiation energy and make the inherent vibration and rotation frequencies of their molecules and atoms consistent with the frequency of far-infrared radiation, resonance or rotation of molecules and atoms is highly likely to occur, resulting in greatly intensified motion. The converted heat energy raises the internal temperature, causing the substance to quickly soften or dry.
The general heating method is to use heat conduction and convection, which requires propagation through a medium, with slow speed and high energy consumption. However, far-infrared heating uses thermal radiation without the need for medium propagation. Meanwhile, as the radiation energy is directly proportional to the fourth power of the heating element temperature, it not only saves energy but also has fast speed and high efficiency. In addition, far-infrared radiation has a certain penetration ability. Due to the absorption of far-infrared radiation energy by heated and dried substances at a certain depth, both internal and surface molecules generate self heating effects, causing solvents or water molecules to evaporate and generate uniform heat, thereby avoiding deformation and qualitative changes caused by different degrees of thermal expansion, and maintaining the appearance, physical and mechanical properties, fastness, and color of the substance intact.
The infrared moisture analyzer is mainly determined by an infrared radiation heater and an electronic balance to determine its accuracy and stability
(Infrared radiation heater: Tungsten wire vacuum tube can emit near-infrared radiation, silicon carbide belongs to long wavelength far-infrared radiation heaters, quartz glass and ceramic infrared heaters can emit mid infrared radiation)
The infrared moisture analyzer is very similar to the infrared moisture analyzer used for heating, drying, and mass determination, which is the standard measurement method for moisture determination. *The "drying reduction method" of the standard measurement method is also known as the (105 ° C5 hour method), (135 ° C3 hour method), etc. It measures the mass change before and after drying by placing the sample in a drying machine for a long time to calculate the water content. For this, it is necessary to determine that the personnel are highly proficient in the equipment and technology. Due to the long time required for measurement, it is difficult to quickly measure a large number of samples. So, for high-precision measurements of a variety of samples, apart from infrared moisture meters, no other options are considered. Although there are also some other electrical and optical measurement methods, they are all instruments that limit the measurement object. From a universal perspective, they are far inferior to infrared moisture meters.
Scope of application: It can be used to determine food related items such as grains, starch, flour, dry noodles, breweries, seafood, fish processing products, edible meat processing products, spices, pastries, heart, dairy products, dry foods, vegetable oils, and industrial products such as drugs, ore sands, coke, glass raw materials, cement, chemical fertilizers, paper, pulp, cotton, and various fibers.
3. Dew point moisture meter:
The dew point moisture analyzer is easy to operate, the instrument is not complicated, and the measured results are generally satisfactory. It is commonly used for the determination of trace moisture in volatile gases. But this method has more interference, and some easily cooled and exchanged gases, especially at high concentrations, may condense before water vapor, causing interference.
4. Microwave moisture analyzer:
The microwave moisture analyzer uses a microwave field to dry samples, accelerating the drying process. It has the characteristics of short measurement time, easy operation, high accuracy, and wide applicability. It is suitable for moisture determination in granular, powdered, and viscous solid samples such as grain, paper, wood, textiles, and chemical products. It can also be used for moisture determination in petroleum, kerosene, and other liquid samples.
5. Coulombic moisture analyzer:
Coulombic moisture analyzerCommonly used to determine the moisture content in gases. This method is easy to operate, has a rapid response, and is particularly suitable for determining trace amounts of moisture in gases. If measured using general chemical methods, it is a very difficult task. However, the electrolysis method is not suitable for the determination of alkaline substances or conjugated dienes.