Best practice in Karl Fischer titration
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- čas přidán 5. 08. 2024
- Extracting all water content, maintaining a pH range between 5 and 7, and avoiding side reactions in the solvent system are critical to the accurate determination of water content in samples.
Doug Clark, National Technical Specialist for Hydranal™ Reagents, has 20 years’ experience with Karl Fischer titration and will help you to:
• Understand the importance of choosing the correct Karl Fischer technique and reagents for different sample types.
• Learn how to optimize Karl Fischer titration for specific sample types.
• Learn how to use standards to verify sample results.
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What is the regent used in karl fischer titration c1
What's the best way to avoid sample (powder) from getting on the side of the walls when transferring?
You mentioned that dimethyl sulfoxide causes a "recovery loss" Can you please explain in some detail how that results? Is the DMSO slowly oxidized to dimethylsulfone? Does partial iodination of methyl group occur?
The DMSO is disturbing the stoichiometry of the KF reaction.
The reaction of water with iodine is shifted from a 1:1 ratio (KF-reaction) to a 2:1 ratio (Bunsen-Reaction).
(KF) H2O + I2 + [RNH]SO3CH3 + 2 RN [RNH]SO4CH3 + 2 [RNH]I
(Bunsen) 2H2O + SO2 + I2 → H2SO4 + 2HI
That means same amount of water require less iodine. That results in reduced consumption and therefore in reduced findings.
The more DMSO is available the worse is the effect.
For more information, download the L141- Water Determination in DMSO laboratory report for free from here: hwll.co/ce3a2
For any additional support, please reach out directly using this form: hwll.co/3unz6
Thank you for your question.
HYDRANAL™ Center of Excellence
Doug, an explanation is provided in the link. Iodide reduces Me2SO to Me2S and water:
Me2SO + 2I- + 2H+-----> Me2S + H2O + I2.
Please check out: www.sigmaaldrich.com/technical-documents/articles/analytical-applications/karl-fischer/water-determination-in-dimethylsulfoxide.html. It is this additional iodine which causes the "loss of recovery" and "shifting" that you mention.
@@GoutamDAS-ls1wb Hi Goutam, Iodine reducing DMSO doesn't explain the low recovery in a Karl Fischer titration. In a KF titration the reaction you mention would be KF neutral since it produces equal amounts of iodine and water. Shifting the stoichiometry towards the Bunsen-Reaction is the reason for the low recovery.
Doug, You raise a valid point. However, I think then in that case, a Swern mechanism might be at work, where the DMSO is oxidizing the MeOH into Formaldehyde and water--where I2 and SO2 serve to activate the DMSO. And so the net reaction would be MeOH + Me2SO -------> H2C=O + Me2S + H2O. Once formaldehyde is formed, it will reduce I2, become an acid, esterify and do all kinds of nonsense. The reaction medium is very hygroscopic and so basically, it is the energy of formation of water which would drive the reaction to the right. I can provide mechanisms if interested
Hello sir please in case if the hydranal is obsolete what's can happen !!?
Most Hydranal™ reagents have a shelf-life between 3 to 5 years during which period we guarantee stable products and highly accurate Karl Fischer titration applications. After the expiry date (as printed on the reagent bottle) is reached however, usability & accuracy of titration is not guaranteed. For further questions please feel free to write into hydranal@honeywell.com.
@@Honeywellprocess Hello sir thanks for the reply , please we have a problem in our karl Fischer the time of conditioning and titration is too long and the apparatus doesn't give us a result in the of the titration it's mentioned that "variable Ep 1 miss" what's can be the problem sir !!!?
@@nisstella Dear Sir, please send over this question and, if you have, any additional information that could help our specialists help with your problem, over email to hydranal@honeywell.com. The Honeywell Research Chemicals Center of Excellence will provide dedicated support. Thank you.