Karl Fischer Method of Moisture Determination for moisture in liquids, or small amounts of moisture in prepared solids.
The Water Determination Test (Karl Fischer Method) is designed to determine the moisture content in substances, utilizing the quantitative reaction of water with iodine and sulfur dioxide, in the presence of a lower alcohol such as methanol, and an organic base such as pyridine.
There are two different determination methods in the iodine-providing principle: the volumetric titration method and the coulometric titration method.
In the volumetric titration method, the iodine required for a reaction with water, is previously dissolved in water, and the moisture content in the sample is determined by measuring the amount of iodine consumed as a result of a reaction with water in the sample.
In the coulometric titration method, first, iodine is produced by electrolysis of a reagent containing the iodide ion, and then, the moisture content in the sample is determined by measuring the quantity of electricity which is required for the electrolysis (i.e., for the production of iodine), based on the quantitative reaction of the generated iodine with water.
The apparatus for volumatric titrations, consists of an automatic burette, a backtitration flask, a stirrer, and equipment for amperometric titration at constant voltage, or potentiometric titration at constant current.
The apparatus for coulametric titration is comprised of an electrolytic cell for iodine production, a stirrer, a titration flask, and a potentiometric titration system at constant current.
The iodine production device is composed of an anode and a cathode, separated by a diaphragm. The anode is immersed in the anolyte solution, and the cathode is immersed in the catholyte solution.
Both electrodes are usually made of platinum-mesh.
KARL FISCHER METHOD MOISTURE DETERMINATION
This volumetric technique involves dissolving the sample in a
suitable solvent and adding measured quantities of a reagent
containing iodine until an end point is reached. This end point
is determined potentiometrically using a platinum electrode.
However, even with the automatic or semi-automatic
instruments commercially available there are certain
problems associated with the technique. These problems
include long analysis time, reagent calibration required, high
reagent consumption rate and large sample amount required.
This technique is still in widespread use today and there are a
multitude of instruments, ranging from simple low cost
manual types, to fully automated titrators.
This coulometric approach to Karl Fischer titration is
becoming more widely accepted in preference to the older