# exchanging H2O in buffer for D2O - pH vs pD?

I have TBS pH 7.4 buffer that I am exchanging all the water out for $\ce{D2O}$. How do I find out what the pD is after all the water is gone? I understand that pH meters don't work for deuterium, and it seems like deuterium also changes the spectral properties of the chromophores in pH paper (or in this case pD paper)

Also, if I want to best mimic the alkaline conditions in $\ce{D2O}$ as $\ce{H2O}$, should pD final = pH initial?

• I'd expect that a pH meter would work, but you'd need to "soak it" in D2O and you'd need a different calibration curve. // Interesting question though! – MaxW Jan 29 '16 at 1:48
• Are you asking how you measure the final pD (to see if you are finished), or how you can determine (for instance, calculate) it? – NH. Dec 28 '16 at 20:39

The articles by Glasoe,[1] Covington et. al.,[2] and (much more recently) Krężel and Bal[3] suggest in their intros that pD values can be obtained from a pH calibrated electrode by adding a correction constant of about $0.4$. This was determined by comparing the measured pH when the same amount of acid or base was dissolved in $\ce{H2O}$ and $\ce{D2O}$.