Karl Fischer

[MJ]

Hello,

I have a question about Karl Fischer Titrations to determine moisture content in samples. I am using Methanol as my solvent instead of pyridine.

I have a basic idea of how a Karl fischer works and have read that products such as ketones (when mixed with methanol as the KF solvent) can product water as a side reaction and therefore effect the results. So my question is this:

Is there a indication or way of telling if a unknown sample will or is producing a side reaction when reacted with methanol in a KF titration. eg does the sample give you a negative signal, or a drift in the end point, or you get a 100% water value etc how can i tell if a side reaction is occuring when my sample is an unknown solid or liquid.

Mike

[DR]

If you are getting very different moisture numbers via KF (which generally eschews pyridine in the indicator solution these days) and an orthoganol method (LOD), I'd be inclined to evaluate the =O content of the unknown via other means (IR scan, wet methods).

[Consumer Products Guy]

I'd guess that most KF reagents these days are pyridine-free, and they titrate faster and better than the pyridine-containing KF reagents. Stuff like Hydranal, AquaStar, etc.

[GaryR]

If you have a side reaction which is producing H2O you will have a drifting end-point, which may never be reached (depending upon your end-point criteria). this will lead to an erroneously high result for water in your sample, or worse, a titration which never ends.
Companies such as Riedel de Hahn offer specialised titrants and solvents for determination of water in ketones and other samples which produce H2O in side reactions. Their web site offers a wealth of information on Karl Fischer titrations. And I'm sure their sales reps would be more than happy to look at your application and suggest some of their products which may be of use to you.

One quick way to see if your getting H2O produced as a side reaction is to perform Std Additions of H2O at several levels. Your results should be linear.

Note: I have no association with riedel de hahn but we do use their KF titrants with good results.

[DR]

^ PS - RDH is now marked as and sold by Fluka (according to the Sig/Ald flyer I got yesterday).

[Markus Laeubli, Metrohm]

Dear MJ

I am the IC not the KF-guy. Anyway Metrohm sells KF equipment and also offers a free booklet on KF.

Do not hesitate to order it.