Hi all,
Is anyone using Ammonium Hydroxide as a high pH buffer?

Yes, to analyze tioconazole.... but the pH of the mobile is higher than 10, so i need to use an up to 12 pH column

Renata

Hi Renata,
What column are you using? I'm currently doing high pH with 10mM Ammonium Bicarbonate at pH 9.0 using a Waters Xterra. At this pH the column has good lifetime to date. Do you buffer the Ammonium Hydroxide back down to 10?

Colin

I also use Xterra, and yes for the second question :o)

Renata

NaOH at high pH buffers only in respect to adding more base. If you add acid there is practically no buffering. (Actually, the buffering on the high side is done by water. I put this into parentheses in the hope that Bill doesn´t see this).

What definition of a buffer is being used here?

Sorry, my eyes must have been crossed...., registered NaOH instead of NH3OH, so saw red.
NH4...whatever, is, of course, a real buffer at pH 10.

Are people using the Ammonium Hydroxide as a high pH buffer and are there any side effects if used at prep scale?

We have used ammonium hydroxide as well as as ammonium bicarbonate for adjusting the pH in the range around pH 9 to 10. For prep, I prefer to use a high concentration of ammonia.

I use buffer NH4OH - NH4OAc pH 10.2 to analyze ranitidine. Ammonia (pKa 9.) is good buffer at pH range 8.2 - 10.2.

i doubt many chromatographers strictly use ammonia in the lab as it's a gas at STP?

Q: if we had an analytical method which required say 20 mM of an ammonium buffer (formate, acetate or bicarbonate) how would we determine the required amount of ammonia (conc. or 25-30% ammonium hydroxide soln.) if moved to a prep system? in other words what's a high concentration of ammonia?

We are routinely running prep methods with ammonium bicarbonate or ammonia. For MS prep applications, you want to stay in the low range: 20 mM ammonium bicarbonate or thereabouts. If you are working with straight ammonia, you can use much higher concentrations, since it is nicely volatile. 100 mM is a good choice.