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Adjusting PH

http://www.chromforum.org/viewtopic.php?t=19667

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Adjusting PH

Posted: Wed Apr 18, 2012 11:07 am
by smartin
Hi,

I would like to prepare a mobil phase with semicarbazide and KH2PO4.
Then, I have to ajust pH at 2,85. What substance I have to use to acidify and basify it?

Thank you!!!!

Re: Adjusting PH

Posted: Wed Apr 18, 2012 10:42 pm
by danko
H3PO4 <–> H2PO4- + H+ pKa = 2.3

Best Regards

Re: Adjusting PH

Posted: Thu Apr 19, 2012 6:09 am
by Markus Laeubli, Metrohm
bringing Danko's equation into words (and more):

a 1:1 mixture of H3PO4 and H2PO4 has a pH of 2.3

In your case, I recommend to measure the pH of the eluent.

eluent pH < 2.85 --> adjust with K2HPO4

eluent pH > 2.85 --> adjust with H3PO4

Re: Adjusting PH

Posted: Thu Apr 19, 2012 7:06 am
by smartin
Thanks a lot for your help!!!!!
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