TEA for negative mode

[Mattias]

I would like to use an LC-method which contains TEA for an analysis in negative mode. I guess the TEA is not a problem for me, but will the other analysts kill me afterwards for contaminating the system? I have heard that it is almost impossible to get rid of.

[Mattias]

Sorry, I should have searched the forum before posting. It seems rather nasty, but on the other hand this is a beautiful separation. Would you just let it go, or give it a try?

[sassman]

We use ethanolamine for our negative ion work. It doesn't seem to interfere with our other analysis (mostly using formic or acetic acid additive). No guarantee it will work for you, though, since our experience is rather limited (MS/MS analysis only with a couple of different methods).

[Mattias]

It should work, unless you get some kind of signal suppression (like with TFA in positive mode).

Do any have experience with signal suppression in negative mode?

[sassman]

After running samples in positive ion mode with formic acid in the mobile phase, the LC system must be purged very thoroughly or we see significant signal suppresion in negative mode. We don't have this problem going from negative to positive since the formic acid concentration (0.2%) is about 10x higher than ethanolamine.

I would imagine that as the concentration of ethanolamine is increased, you would eventually get suppression at some point. In our case, 2mM ethanolamine is enough to greatly increase response. Increasing this concentration up to 10mM does not seem to help much more. I haven't tried increasing beyond that because the pH begins to climb beyond what most columns can handle.

A whole book could be written on signal suppression caused by matrix components (and probably has), but usually this can be minimized by good chromatographic separation and careful choice of mobile phase additives.

[weber]

We had some very bad experience with TEA! I would strongly encourage you NOT to use it, unless the machine ist used only in negative ESI.
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Matthias