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ph of mobile phase containg water:methanol:o-phosphoric acid
Posted: Wed Dec 12, 2012 7:33 pm
by chilam
Hi,
what is pH of ph of mobile phase containg water:methanol:o-phosphoric acid (60: 20:20).
when i prepared mobile phase pH its going down to 2.6. But accourding to paper it should be 4.4.
Can you give me suggestions
Re: ph of mobile phase containg water:methanol:o-phosphoric
Posted: Thu Dec 13, 2012 6:16 am
by Markus Laeubli, Metrohm
Dear chliam
For me that pH = 4.4 looks more like NaH2PO4.
pH = 4.4 is almost in the middle of pKa1 and pKa2 of phosphoric acid.
Re: ph of mobile phase containg water:methanol:o-phosphoric
Posted: Thu Dec 13, 2012 3:02 pm
by tom jupille
water:methanol:o-phosphoric acid (60: 20:20)
20% phosphoric acid ?????
Re: ph of mobile phase containg water:methanol:o-phosphoric
Posted: Thu Dec 13, 2012 3:17 pm
by chilam
i am using 0.1% of phosphoric acid
Re: ph of mobile phase containg water:methanol:o-phosphoric
Posted: Thu Dec 13, 2012 3:28 pm
by bisnettrj2
When are you measuring the pH? Before or after the addition of methanol?
Re: ph of mobile phase containg water:methanol:o-phosphoric
Posted: Thu Dec 13, 2012 5:15 pm
by chilam
i am measuring ph after preparing complete mobile phase ( water:methanol:0.1% phosphoric acid)
Re: ph of mobile phase containg water:methanol:o-phosphoric
Posted: Fri Dec 14, 2012 12:12 am
by bisnettrj2
Measure the pH before the addition of the methanol, see if it's different.