Karl Fischer Titration – Defined? or Over Simplified?
Posted by Art Gatenby on Mon, Jan 19, 2009 @ 03:42 PM
Often I’m asked “What is Karl Fischer titration?” I’m always somewhat reticent to answer. If I can’t quickly change the subject I revert to a simple explanation, that even I (being somewhat challenged as a chemist) can understand. The explanation seems to help the novice understand Karl Fischer.
However, I’m always waiting in terror for the inquirer to expand the question and ask me to explain the chemistry, which is complex and goes well beyond my comprehension.
Soooo——- I’m gong to unmask my rudimentary definition.
I start by saying that I place a solvent in a sealed vessel (container) that is void of water. In this vessel is an electrode that has two electrical leads. A meter is attached between these leads. When the solvent in the vessel has no water, the resistance between the leads is very high. A sample is inserted that contains water. The water significantly lowers the resistance and the meter moves off the zero water point.
We now add a reagent to the vessel. The reagent reacts with the water to produce (And here comes my leap over the complex chemistry) a new chemical that has a high resistance. We add the reagent until the meter returns to its starting position (zero water point).
We measure the amount of reagent used. That measurement tells us how much water was in the sample.
The reagent that produces that complex chemical reaction is called a Karl Fischer Reagent. As one might guess, the reagent and procedure was invented by Karl Fischer, a chemist. Karl Fischer Titration has became synonymous with the measurement of water content.
There are two equipment techniques that perform this test. They are called Volumetric Karl Fischer and Coulometric Karl Fischer. In future musings we will explain the pros and cons of each.
If any of you are conversant with the Karl Fischer chemistry and would like to to share it, please comment on this post.
Art