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ion pairing with HFBA question
Posted: Tue Oct 07, 2014 7:14 pm
by Mike H.
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?
Re: ion pairing with HFBA question
Posted: Mon Oct 13, 2014 6:03 am
by Markus Laeubli, Metrohm
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.
Re: ion pairing with HFBA question
Posted: Tue Oct 28, 2014 4:22 pm
by MaryCarson
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.
Re: ion pairing with HFBA question
Posted: Mon Sep 21, 2015 11:35 am
by ljc
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.
Re: ion pairing with HFBA question
Posted: Tue Dec 14, 2021 12:02 pm
by Enriqueta
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