What is Karl Fischer titration?
Karl Fischer titration is a traditional titration method in analytical chemistry to determine amounts of water in a sample by using coulometric or volumetric titration. It was first performed in 1935 by the German chemist Karl Fischer[1]. The titrimetric method for water determination is based upon the quantitative reaction of water with an anhydrous solution of sulfur dioxide and iodine in the presence of a buffer that reacts with hydrogen ions. Nowadays the titration is usually done with an automatized Karl Fischer titrator.
What is the principle of Karl Fischer titration?
The mechanism of Karl Fischer titration mainly involves two reactions. In the first step, the alcohol (usually methanol or ethanol), sulfur dioxide and a base react to form an alkylsulfite intermediate. After that, the alkylsulfite reacts with iodine and the water from the sample. At the equivalence point, water and iodine are consumed in equimolar amounts. As a result, the amount of water present in the sample can be calculated depending on the amount of iodine.
How many types of Karl Fischer titration?
There are two types of Karl Fischer titration, including volumetric titration and coulometric titration. The difference between them is in the way that how iodine is generated. The iodine is included in the reagents during volumetric titration while it is generated at an electrode in during coulometric titration.
- Volumetric KF
Volumetric KF analysis involves slowly adding the titration solution to the sample, while a set of electrodes measures the current that can flow through the solution. Once all the water has reacted, the voltage drops significantly as the iodine becomes "excess". Volumetric KF is the ideal method for measuring higher concentrations of water.
- Coulometric KF
As for coulometric KF, the titration solution is premixed in the chamber and already contains all components, including iodine in the form of potassium iodide. By applying a small current, it is slowly converted to iodine, allowing the titration to take place. Coulometric KF is usually more suitable for measuring very low water concentrations and is more accurate than volumetric analysis.
Karl Fischer titration service at Creative Proteomics
Creative Proteomics provides Karl Fischer titration services to determine water content in both liquid and solid materials. Our laboratory is equipped with both volumetric and coulometric titrators, and an oven attachment for analysis of solids. Customers may choose different types according to following tips:
The titration equipment : Standard titration set up
The water levels in the sample:
Volumetric titration: 0.1-100% H2O
Coulometric titration: 0.001-5% H2O
Sample requirements and preparation
Acceptable matrices: Suitable liquid and solvent samples can be tested as is, through injection into the KF titration chamber
Sample size: 20 grams
Information required: Please supply expected estimates for each sample
Why choose us?
- Many years of experience in the determination of water by Karl Fischer analysis
- All testing is performed in humidity controlled laboratories
- Quick turnaround time on Karl Fischer testing
- High quality service experience and timely feedback to project progress
Creative Proteomics is committed to keeping our methods and limits of detection up to date according to the latest standards and qualifications. Please contact us if you have any questions regarding detection limits/quantitation limits or method references. Our professional team is happy to assist you.
Reference
- Neues Verfahren zur maßanalytischen Bestimmung des Wassergehaltes von Flüssigkeiten und festen Körpern. Fischer Karl, Angew. Chem., 1935, 48 (26).
