Buffers for HPLC stable at pH 8.0

[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

[tom jupille]

Alkaline buffers absorb atmospheric CO2. Keep your buffer bottle closed with a CO2 trap in the vent to atmosphere.

[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.

[Uwe Neue]

I ran into exactly the same problem, and I do not have a really solid solution. Mark's suggestion is worth exploring.

[Hassel Hoff]

triethanolamine has a pKa of 7.8 and is MS compatible. Simple and perfect for bufferiing at pH 8.

[Uwe Neue]

Triethanolamine sounds like an idea worth exploring. Let us know if it works for you!

[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

[Uwe Neue]

As the counterion and for adjustment of the pH, I would use formic acid or acetic acid.

[Chris Pohl]

Hassel Hoff,

Are you sure Triethanolamine in MS compatible? It's boiling point is ~200C at 5mm Hg!