[artsjeroen]

For the assay determination of piperazine citrate (acc. Ph.Eur) a non-aqueous titration is described.
Normally this potentiometric titration is no problem at all. But today I performed several titrations and all titration results are about 4% too low. Even old batches that are already released are about 4% too low when I reanalyse them.

The standardization of the perchloric acid 0.1 M gave no problem at all. So my first thought was that the addition of HClO4 was too fast. However, slow addition of HClO4 gave similar results.

Slightly heating the solution to dissolve the piperazine citrate and then adding glacial acetic acid gave slightly higher results. This has never been necessary before (for the same manufacturer) to get the results right.

(The same reagents/titrant/electrode etc. were used during the analysis and standardization)

The electrode I use is a Pt-ring electrode, which is one week old.

I am out of options, maybe someone on this forum has an idea about solving this problem?
Thanks in advance!

[artsjeroen]

Problem solved!  I did not use enough solvent (glacial acetic acid). More solvent gave correct results.