ion pairing with HFBA question

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I'm trying to do a separation using hexafluorobutyric acid. I have adequate k', but the peak is tailing and I think this may be because the pH is lower than the pKa of the compound. I'm not certain this is the case for the tailing, but I can't think of another reason for it at present. Can HFBA be adjusted to pH 2.8 and if it can what would be an appropriate reagent to do this with?
I do not have a lot of experience with ion-exclusion. But I do not see a big problem of adjsuting the the pH. I would try simple NaOH.
Just give it a try.
Dr. Markus Laeubli
Manager Marketing Support IC
(retired)
Metrohm AG
9101 Herisau
Switzerland
I assume you are using heptafluoro, not hexafluorobutyric acid. How much HFBA is in your mobile phase? Years ago I developed an aminoglycoside method with HFBA. I started out with 5 mM (no pH adjustment), and had some success. However, when I increased the HFBA to 20 mM, peak shape improved considerably for some of the AGs. HFBA concentration in the tissue extracts remained at 5 mM.
All standard disclaimers apply. My posts are my opinions only and do not necessarily reflect the policies of my employer.
The pH HAS to be less than the pK of your analyte if you're doing exclusion. So raising the pH wouldn't help you there. But if your analyte is a cation, the HFBA is acting as an ion pairing agent. In that case raising the pH makes sense. Would need more info about your analyte and sample matrix, column, etc.
Hi,
I am using HFBA 0.1% because my compound is a peptide rich in Lysines and it would not be retained on the column without HFBA, for this reason I used HFBA (as ion pairing reagent). I tested TFA but is was not ok. The pH is around 1.0, and the pH range for this column is 1-11.
Thanks for your help
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