The difference between volumetric method and electric quantity method of moisture analyzer
The moisture determination method has been recognized as the most accurate method by many standards, such as ISO, ASTM, DIN, BS, and JIS. It is suitable for the determination of the moisture content of various substances. It is the current moisture analysis measuring instrument. The Karl Fischer method was proposed by Karl Fischer in 1935, using I2, SO2, pyridine, and anhydrous CH3OH (with a water content below 0.05%) to prepare a reagent, and determine the water equivalent of the reagent. After the reaction, the water content in the sample is calculated by calculating the consumption of reagents. The standardization organization defines this method as the standard for measuring trace moisture, and our country also defines this method as the national standard for measuring trace moisture.
Petroleum products have a certain degree of water absorption, which can absorb and dissolve part of the water from the atmosphere or when in contact with water. There are three main states of water entering petroleum products: 1. Suspended state: water is suspended in the oil in the form of water droplets. It mostly occurs in heavy oil with high viscosity. 2. Emulsified state: refers to the water is evenly dispersed in the oil in the form of very small water droplets. 3. Dissolved state: the water exists in the state of being dissolved in the oil. The amount it can dissolve in oil depends on the chemical composition and temperature of petroleum products. Generally, the ability of halene, cycloalkane and olefin to dissolve water is weak, and aromatic hydrocarbon can dissolve more water. The higher the temperature, the more water can dissolve in the oil. So a Karl Fischer tester is needed to measure the water content in it.
Determination methods include volumetric method and coulometric method
1. Karl Fischer volumetric method (titration method) every time a sample is measured, the following five basic steps must be carried out: 1. First inject a part of the solvent into the titration tank; 2. Titrate a part of the Karl Fischer reagent to balance it; 3. 1. Inject the sample to be tested; 4. Titrate the Karl Fischer reagent into the titration tank; 5. Discharge the waste liquid. Simply put, the reagent should be replaced every time a measurement is made. This method is based on the amount of Karl Fischer reagent injected and the titer of the reagent to convert the moisture content, because the Karl Fischer reagent is affected by factors such as environmental humidity, light and sealing, and the titer changes at any time, which leads to the determination of error. During the measurement test, every time a measurement is made, the waste liquid used last time must be discharged and re-titrated with a new Karl Fischer reagent, which will pollute the environment, consume a lot of reagents, and the operation is very cumbersome and the measurement accuracy is low. The automatic volumetric moisture analyzer also needs the above five basic steps, but adds functions such as automatic titration and automatic waste discharge.
2. The Karl Fischer coulometric method (electricity method) trace moisture analyzer is in the case of electrolytic cell balance, only one operation step is required, which is to inject the sample, and the instrument will automatically perform electrolysis according to the water content in the sample to make it After the equilibrium is reached again, the moisture content is converted according to the electricity consumed by electrolysis, and the result is digitally displayed on the instrument, so the precision and accuracy are higher and the measurement speed is faster. The reagents of the coulometric method can be used continuously for a long time once added, and do not need to be replaced frequently. The consumption of reagents is low, the cost of determination is low, and the operation is simple.
