The Karl Fischer titration (or KF titration or simply KF) is the classic analytical method used to detect water, and is convenient to use. The basis of the Karl Fischer titration is the reaction of water with iodine and sulfur dioxide. In the early develop of this analytical technique, the solution containing water was titrated with a solution of I2 in benzene or MeOH until the I2 color remained, providing a sharp, reproducible endpoint to determine the water content. Today of course benzene is avoided as a solvent for the laboratory and scale-up, and less toxic solvent or solvent mixtures are used. The accurate and rapid coulometric assay, which can detect down to 10 micrograms of water, is generally preferred, I2 is generated elctrolytically at the cell anode, and the amount of water is determined by the current required for electrolytic oxidation of HI.My favorite thing about Karl Fischer is that it's a machine that spits out a number (assuming your molecules are compatible with the reagents, that is.) How much water is in there? You can find out, instead of the whole "I dunno, it's wet, I think." I highly recommend them.
Wednesday, October 21, 2015
Process Wednesday: Karl Fischer titration
From the second edition of "Practical Process Research and Development" by our mentor-by-literature Neal Anderson, a lovely little section on the determination of water content by Karl Fischer: