Hi all,

I wonder what are your favourites buffers for LC-MS when acidic or neutral or basic pH is desired and when positive or negative ion-mode is required. Is there a list with all volatile acids and bases that can be used? Are there any of these acids /bases that you don’t work with, due to other problems such as ion-suppression etc? What are the maximum concentrations that you use these buffers?

Thanks for your input,

Mark

In the acidic range, you can use formic acid, acetic acid, and even TFA at low concentrations. For buffers, ammonium formate and acetate at the respective pKa of formic acid and acetic acid. In the alkaline pH we use mostly ammonium bicarbonate or ammonia at low concentrations. We have used ammonium bicarbonate neutralized with formic or acetic acid for pH 7.
Typical concentrations are 10 mM, but 20 mM is not impossible.

Hi Mark,

You might have a look in one of our last articles (speaking when I was still in France, actually I'm in the USA), which deals with mobile phase additives, volatile enough to be used with mass spectrometry. In this study we have evaluate several acids and bases based on their response on the evaporative light scattering detector. Among them 10 volatile acids and 10 volatile bases as well as their corresponding salts are evaluating in different concentrations. The results are summarized in a colour semi-pyramid table where depending on their volatility (non volatile, volatile up to 5 mM, volatile up to 25 mM the acids, volatile at least up to 100 mM) acids, bases and salts are marked with different colours.

The article has been published in LC GC Europe 15, (2002), 98-102 (title: Volatility evaluation of mobile phase/electrolyte additives for mass spectrometry), I know that the American couldn't have access up to now. You may now found the article on line in the new LC GC Europe site on http://www.lcgceurope.com/lcgceurope/data/articlestandard/lcgceurope/062002/9090/article.pdf. I have a pdf file of a better quality than the one provided on-line that I could send you upon request.

About additives that I wouldn't work with is maybe triethylammine due to its persistent memory effects once used in the mobile phase. I have a relative article somewhere that I could send you upon request. We get rid of it by operated our heated nebulizer overnight in high temperatures.

Hope the above helps,

Kostas