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View from Inside a Karl Fischer Titration Cell.

Posted by Art Gatenby on May 17, 2010 4:26:00 PM

 When people are looking for a way to measure small amounts of moisture, we often recommend the Karl Fischer method.

The first question many ask is
"What is Karl Fischer?"
The second question usually is
"How does it work?"

I thought it might be interesting to answer the second Karl  Fischer Titration Vesselquestion from the perspective of actually being inside the Karl Fischer Titration Cell.

First, I climbed into a jar that has four openings at the top.

 Through one of theKarl Fischer Generator Electrode openings, an operator pushed a glass tube with a funny kind of mesh at the bottom. They call this the Generator.

Next, through another opening, they push a second glass tube that has wires sticking Karl Fischer detector Electrodeout of the bottom. They call this the Detector.

Sitting at the bottom of this jar is a little rod, which they call the Stirrer.

Comfortably sitting on the stirrer rod at A Karl Fischer Stirrer Rodthe bottom of the jar, I observe an operator pouring a liquid into the top of the generator above the funny mesh.

Then, they tell me to be ready to swim as they fill the main part of the jar about halfway with another liquid they refer to as the Reagent. As I'm treading water in this reagent, they seal off all the openings so they are air-tight.

They yell down that they are going to start clearing out all ofInside Karl Fischer Test the moisture from inside the jar. The stirrer bar starts spinning, causing chaos in the reagent. I feel like I am in a Waring Blender.

As I'm bouncing around the jar -- or as the operators call it the Titration Cell -- they tell me to be ready for a little shock. They turn on the machine and the detector says, "Hey! There is water in here. Push some electric current into the cell." Zap Zap Zap.......

The maelstrom starts to turn yellow. What is this? It is a whole bunch of Iodine; the very same substance you used to put on a cut finger.

They tell me that the shock I felt caused the Reagent to produce the Iodine. Apparently, the Iodine reacts with the water and gets rid of it.

By that time, the detector says, "Water's All Gone" and they turn off the stirrer. I'm almost drowned.

An operator yells down, "Here comes a real test!" The dammed stirrer starts and I'm in the blender again.

NKarl fischer  syringeow I see the business end of a syringe - the needle. The syringe pushes the sample to be tested into this chaotic whirlpool in the cell and the shocks start again. Zap Zap Zap... The detector found water.

I'm racked with shocks for a minute or two and the yellow returns. The Iodine does its job and the detector says, "No More Water."

The shocks stop. The test is over. The operators shut down the stirrer and pull me out --- totally waterlogged. Or should I say reagent-logged?

The machine measured the amount of shock it took to generate enough Iodine to get rid of the water. All of this was done just to measure a few micrograms of water.

I hope you found this amusing and maybe a little informative.  If you found this useful, share it with associates who deal with moisture measurement.

By the way, I am never going inside a Karl Fischer Titration Cell again.

A very soggy Art

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Topics: Karl Fischer, Karl Fischer Titration

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