Page 1 of 1
Buffers for HPLC stable at pH 8.0
Posted: Thu Apr 13, 2006 5:08 am
by Teresa
I am developing a method using xbridge column and found that for the best separation the optimum pH to use to be 8.0-8.1 using NH4HCO3 adjusting pH with NH4OH and/or Formic acid. Other buffers used to prepare pH 8.0 were combination of NH4Formate, Formic acid, NH4OH, TFA. However pH 8.0 could not be maintained in all the buffers prepared. pHs can vary by 0.2 pH unit the next day.
The buffers required to be LC/MS compatible.
Has anyone been able to prepared a stable buffer at around pH 8.0? Please assist.
Teresa
Posted: Thu Apr 13, 2006 5:30 pm
by tom jupille
Alkaline buffers absorb atmospheric CO2. Keep your buffer bottle closed with a CO2 trap in the vent to atmosphere.
Posted: Thu Apr 13, 2006 8:06 pm
by Mark Tracy
An ammonium bicarbonate buffer will outgas CO2 and NH3. I used to use vacuum degassing to tweak the pH upward on these buffers. So... Don't degas the buffer; make it fresh daily.
Posted: Thu Apr 13, 2006 8:31 pm
by Uwe Neue
I ran into exactly the same problem, and I do not have a really solid solution. Mark's suggestion is worth exploring.
Posted: Thu Apr 13, 2006 10:34 pm
by Hassel Hoff
triethanolamine has a pKa of 7.8 and is MS compatible. Simple and perfect for bufferiing at pH 8.
Posted: Fri Apr 14, 2006 12:23 am
by Uwe Neue
Triethanolamine sounds like an idea worth exploring. Let us know if it works for you!
Posted: Fri Apr 14, 2006 7:23 am
by Teresa
Thanks for all your suggestions.
Triethanolamine is definitely worth trying. We have this and Tris in mind to try out. What would you suggest appropriate to use for adjusting pH?
I will try them after the easter holidays.
teresa
Posted: Fri Apr 14, 2006 2:17 pm
by Uwe Neue
As the counterion and for adjustment of the pH, I would use formic acid or acetic acid.
Triethanolamine for MS?
Posted: Fri Apr 14, 2006 10:47 pm
by Chris Pohl
Hassel Hoff,
Are you sure Triethanolamine in MS compatible? It's boiling point is ~200C at 5mm Hg!