Measuring pH in 95% DMSO solutions?

[jsp at bio.auc.dk]

Hi there,

I'm trying to make a 95% DMSO, 4.5% H2O, 0.5% CH2ClCOOH solution at pH 5, by adjusting pH with HCl.

Im using a standard pH-meter (Hamilton minitrode), but I can't seem to get stable readings due to the low water activity. If I clean the electrode and re-introduce it into the DMSO solution I get a completly different reading. Does anyone have a good suggestion how to accurately measure the pH?

Kind Regards,

Jesper S. Pedersen
Aalborg University
Denmark.

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