Measuring pH in 95% DMSO solutions?

Dr Engelbert Buxbaum engelbert_buxbaum at web.de
Mon Nov 4 07:35:33 EST 2002


jsp at bio.auc.dk wrote:

> 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?


pH electrodes do not work in organic solvents. The way I used to do this
is to make an aqueous buffer, adjust the pH and then add the solvent.
This will of course change the pH, but at least the results will be
reproducible.



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