By Anonymous on Tuesday, June 8, 2004 - 07:29 pm:
Dear experienced LC-MS users,
I get a group peaks with a same interval in ES- mode. Peaks distributed at 249, 385, 521,657, 792,928..., with regularly increasing 136. Anyone could tell me what moeity this is.
Thank you very much.
Michelle
By Anonymous on Friday, June 11, 2004 - 12:24 pm:
Michelle,
The repetitive ions with a difference of 136 daltons is due to sodium trifluoroacetate (NaTFA). You likely have trifluoroacetic acid in your mobile phase and you are observing NaTFA clusters of the trifluoroacetate ion (m/z 113) in negative ion ESI-MS mode. I would strongly suggest removing TFA from your mobile phase, since is has been well documented that TFA will suppress ion formation of your analytes in negative ion ESI-MS mode. Try instead using either acetic or formic acid if your LC method requires an acid modifier.
Kevin
By MG on Friday, June 11, 2004 - 03:22 pm:
If TFA were present, a strong signal at 113 would also be observed, if you are scanning that low.