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Progress in pulsed-current Karl Fischer coulometry using diaphragm-free cells
1Department of Chemistry, Umeå University, Sweden.
Fresenius' Journal of Analytical Chemistry
|February 28, 2001
Summary
Home-made Karl Fischer reagents improve water determination accuracy compared to commercial ones. Optimized parameters like current density and titration rate are crucial for precise results with pulsed current coulometry.
Area of Science:
- Analytical Chemistry
- Electrochemistry
Background:
- Karl Fischer (KF) coulometry is a standard method for water determination.
- Diaphragm-free, pulsed current KF coulometry offers potential advantages but requires optimization.
- Reagent composition and reaction byproducts can influence accuracy.
Purpose of the Study:
- To investigate factors affecting accuracy in diaphragm-free, pulsed current Karl Fischer (KF) coulometry using the Metrohm 756 instrument.
- To compare the performance of commercial KF reagents with specially designed home-made reagents.
- To identify critical parameters for optimizing water determination accuracy.
Main Methods:
- Comparison of commercial (Riedel-deHaen, Merck) and home-made KF reagents.
- Investigation of home-made reagents buffered at pH 10 with modifiers (chloroform, hexanol, ethylene glycol).
- Evaluation of cathode current density and titration rate effects on accuracy.
- Comparison of pulsed current KF coulometry with continuous coulometry.
Main Results:
- Home-made KF reagents showed significantly lower positive errors (0.2-1%) compared to commercial reagents (2-5%).
- Optimized parameters included a maximum generator current of 400 mA (1,400 mA cm(-2)) and a titration rate of 2,000 µg min(-1).
- Pulsed current KF coulometry, even under optimal conditions, exhibited slightly larger errors than continuous coulometry.
Conclusions:
- Home-made KF reagents, optimized for reduced byproduct formation, enhance accuracy in pulsed current coulometry.
- Cathode current density and titration rate are critical parameters for accurate water determination.
- While optimized, pulsed current KF coulometry showed slightly lower accuracy than continuous methods.
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