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Method Selection for Moisture Determination in Chemical Products:
In many liquid chemical products and intermediates, moisture content is one of the key indicators of product quality. Excessive moisture can disrupt chemical reactions, generate by-products, and reduce yield.
Testing Basis
GB/T 6283-2008 Determination of Water Content in Chemical Products - Karl Fischer Method (General Method)
Testing Scope
This standard specifies the general method for determining free water or crystalline water content in samples using the Karl Fischer visual and coulometric methods. It is applicable to the determination of free water or crystalline water content in most organic and inorganic solid and liquid chemical products. It is not applicable to samples that can react with the main components of the Karl Fischer reagent to produce water or samples that can reduce iodine or oxidize iodides.
Principle
Any water present in the sample (free water or crystalline water) quantitatively reacts with the Karl Fischer reagent (a solution composed of iodine, sulfur dioxide, pyridine, and methanol) of known titer.
Note: Methanol can be replaced by ethylene glycol monomethyl ether. Using this reagent allows for more consistent titration volumes and enables the determination of moisture in certain aldehyde and ketone chemical products without the need for specialized techniques.
Karl Fischer Volumetric Moisture Determination Process
In Karl Fischer volumetric moisture analyzers, there are several types available, with differences in connections and measurements, but the basic determination process is similar. The process is as follows:
1. Eliminate Solution Blank
Add 10-15 ml of anhydrous methanol reagent to the reaction cell (submerging the electrode), open the burette to start dispensing, and inject the Karl Fischer reagent into the reaction cell until the trace moisture in the methanol is completely reacted. The instrument will automatically stop and emit an alarm sound.
2. Calibrate Karl Fischer Reagent
Press the zero reset key, use a 10 μl sampler to take 10 mg (10 μl) of distilled water and place it into the reaction cell. Press the titration start key, and the instrument will begin automatic titration. When the endpoint is reached, the buzzer will sound, and the endpoint indicator light will illuminate. The digital display will show the volume of Karl Fischer reagent consumed by the 10 mg of water, allowing the calculation of the amount of water consumed per milliliter of Karl Fischer reagent.
F = 10 / A
Where: F - amount of water consumed per milliliter of Karl Fischer solution; 10 - mass of water taken (mg); A - volume of Karl Fischer reagent consumed during titration.
3. Determine Moisture Content
Press the zero reset key, use a sampler to take 10 ml of the sample to be tested, and add it to the reaction cell. Press the titration start key to begin titration. When the endpoint is reached, the buzzer will sound, and the endpoint indicator light will illuminate. The result is calculated as follows:
Moisture Content = A1 × F / 10000
Where: A1 - volume of Karl Fischer solution consumed by the sample; F - mass of water consumed per milliliter of Karl Fischer reagent; 10000 refers to the mass of the 10 ml sample added.
Reagents are required during the operation, so protective measures must be worn during the process.