Generator electrodes – with or without frit – which is better?

Most manufacturers use a similar configuration of titration cell in which the anode and cathode compartments are separated by a frit (diaphragm) and each compartment is charged with different reagents. Some companies now offer fritless generator electrodes for use with single solution coulometric reagents.

Probably the most widely available coulometric reagents are the Riedel de Haën Hydranal Coulomat products. They are used with the majority of commercial coulometers. Some coulometer manufacturers promote the fritless electrode configurations and single solution coulometric reagents, such as Hydranal Coulomat AG, as being preferable to the fritted type for many applications including for oil samples.

Although the ASTM and other methods stipulate using separate coulometric anode and cathode reagents in conjunction with fritted electrodes, we decided to ask the leading Karl Fischer formulation specialists for their opinion, especially with regard to crude oils and transformer oils samples.
Their replies stated;

“Hydranal Coulomat AG is not to be recommended for crude oil because it is very important to dissolve the tar in the crude oil in order to avoid a coating of the platinum pins. Using solubilizers such as chloroform or xylene in a reagent, it is necessary to use a cell with diaphragm (frit).”

On the subject of transformer / insulating oils they stated;

“Water content of approx 10ppm have to be analysed carefully and we would also prefer a cell with diaphragm (frit) and a reagent containing chloroform.”

It would appear that they agree with our long held opinion that coulometric generator electrodes which have a frit separating the anode and cathode chambers, in conjunction with separate anode and cathode reagents such as Cou-Lo Formula reagents, are much better for these applications. All Aquamax KF titrators are supplied with fritted type of electrode unless otherwise requested on the order.

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