-
E-mail
2757649502@qq.com
-
Phone
13853336388
-
Address
No. 641, 6th Floor, Jinshi Licheng Street Public Building, No. 136, Communist Youth League West Road, Zhangdian District, Zibo City, Shandong Province
Zibo Coulomb Analysis Instrument Co., Ltd
Comparison of Applicability between Karl Fischer Capacity Method and Karl Fischer Moisture Analyzer
Date: 2025-10-10Read: 0
Karl Fischer method is a method for determining moisture content, and its modern automated instruments are mainly divided into Coulomb method and volumetric method. Although the principles are the same, there are significant differences between the two in terms of measurement principles, measurement ranges, and typical applications, which directly determine their applicable scenarios.
Core difference: Measurement principle and range
Karl Coulomb method:
Principle: Based on electrochemical electrolysis. The instrument generates iodine in situ (2I ⁻ → I ₂+2e ⁻) by electrolyzing Karl Fischer reagent (containing iodine ions) in the titration cell, and the generated iodine immediately reacts with the moisture in the sample. At the endpoint of the reaction, the instrument calculates the absolute mass of water directly by accurately measuring the total amount of electricity consumed by electrolysis according to Faraday's law.
Range: Designed specifically for trace to low levels of moisture, the typical measurement range is between 1 μ g (microgram) and 100mg (milligrams) of moisture. It has high sensitivity and a resolution of up to 0.1 μ g.
Karl Fischer Capacity Method:
Principle: Based on classical titration. The instrument adds a known concentration of iodine titrant to the external part of the Karl Fischer reagent containing the sample through a burette. By detecting the endpoint of titration (such as the double platinum electrode permanent stop method), the moisture content is calculated based on the volume of titrant consumed and its accurate concentration.
Range: Suitable for medium to high moisture content, with a typical measurement range from 100ppm (approximately 0.01%) to 100%.
Applicability Comparison and Selection Guide
Based on the above core differences, the applicable scenarios of the two are clear and distinct:
Select based on moisture content:
Coulombic method: When the moisture content of the sample is extremely low (usually below 50-100mg, or concentration below 1%), the Coulombic method must be selected. For example, measuring trace amounts of moisture in transformer insulation oil, polymer particles, specialty gases, lithium battery electrolytes, etc. The volumetric method in this range will experience a sharp increase in relative error due to the small consumption volume of titrant.
Capacity method: When the moisture content of the sample is high, the capacity method should be selected. For example, measuring samples of drug raw materials, some chemical liquids, food, etc. with a moisture content ranging from a few percent to several tens of percent. The volumetric method has a fast analysis speed and the cost of a single measurement is usually lower than that of the Coulomb method.
Select based on sample morphology and properties:
The Coulomb method requires high accuracy in sample introduction and is more suitable for accurately weighing or quantitatively introducing liquids and solids.
The volumetric method is relatively flexible in sample processing and can handle insoluble solids through accessories such as heating furnaces. It is applicable to a wider range of sample types, but attention should be paid to the solubility and side reactions of the sample in the reagent.
The Coulomb method and the capacity method are complementary rather than competitive.Coulombic method is a trace water analysis method known for its absolute measurement and high sensitivity; The capacity rule is an efficient and economical choice for measuring medium to high moisture content. The primary basis for correct selection is the estimated moisture content in the sample, followed by the sample matrix and possible interference factors.
