Combining coulometry with the Karl Fischer titration can provide many advantages over the volumetric technique. The main benefits that this coulometric technique offers include higher sensitivity, faster titrations, no reagent calibration required and economical operation. Indeed, unlike volumetric instruments where the solvent mixture is normally replaced after each titration, coulometers can determine the water content of multiple samples on one single charge of reagent.
The criteria governing reagent life are threefold:
The physical size of the titration cell usually allows for 50 – 60 ml of sample to be added. Sample volumes of 0.1 – 2.0 ml are typical for most oil and petroleum products therefore the maximum volume of 50-60 ml is not usually a limiting factor.
The second criteria governing reagent lifetime is the total amount of water that can be analysed before saturation. A standard charge of 100ml anode reagent can usually analyse upto 1 gram of water. Considering that the injected sample volume is normally quite small, and that usually the analysis is for the determination of low levels of water, then this water capacity should not become a limiting factor either.
Similar to all other Karl Fischer reagents, coulometric reagents deteriorate when left out in sunlight and with increases in temperature. Life expectancy for one charge of reagents when left in the titration cell can be 2-3 weeks although this is also dependent on the total amount of sample injected and the amount of water titrated.
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