What is this contaminant with m/z @ 248.9718 (+/- 0.0010)?
Have you seen this ion? What is it?
Instrument: Agilent 6550 Q-TOF;
In ESI negative mode;
Water/Acetonitrile as mobile phase;
The background ion was observed through the run, with much stronger signal at higher pH (0.05% NH4OH).
Similar to TFA dimer sodium adducts (248.9604), the ion has a negative mass defect and low abundance for the A+1 isotopologues, but the measured m/z for the contaminant ion does NOT match the m/z of TFA dimmer sodium adduct (248.9718 vs 248.9604). The measured m/z should be quite accurate (appropriate signal intensity, repeated detection right after tuning).
Thank you very much for your comments
Hi, most probably it is a signal from trifluoroacetic acid (TFA) cluster. It is highly common if you use NaTFA as calibrant or TFA in mobile phase, regards.
Thank You Eduardo.
The following could be expected from TFA adducts (negative mode):
CF3COO- --> 112.9856
CF3COONa.CF3COO- --> 248.9604
But I did not see those.
Instead, m/z 248.9718 ion was observed, and that's what puzzles me.
Also, product ion spectrum shows little fragments, suggesting the likelihood of metal ion adduct formation.
Can you tell us more about the isotopic distribution, especially some accurate numbers for mass and relative intensity?
Is this a spectrum of the moleclar ion or a product ion? Also, is it positive ion mode or negative ion mode?
If we assume it is a mass spectrum of the molecular ion then we see an immediate problem. The isotope pattern suggests that the compound could contain three carbon atoms, but it is it is hard to get to a molecular weight of 249 if there are only three carbon atoms. If there are three carbon atoms then the isotope distribution also suggests that there might be a lot of mono-isotopic elements in the formula, or at least elements that don't have a high abundance of a +1 Dalton isotope. Is there any other information you can give us?
There is also the negative mass defect to explain. This suggests that there are few if any hydrogen atoms in the molecule.
Hello Lan Liu , the contaminant peak 248.973 remains to be a mystery to me, although I have had better luck with some other "weird" ions observed. Sorry for not having a better answer for you.
Since multiple people have reported the same odd ion, it must be real and will show up under certain condition or scenario.
I have this unknown contamination since many years in Agilent 1200 HPLCs.
Finally I may have found an answer here:
https://community.agilent.com/technical/lcms/f/forum/5480/how-do-we-get-rid-of-identify-contamination-with-m-z-248-9737-negative-mode
It's probably a gold complex [Au(CN)2]- that can stem from impurities in the ACN reacting with gold parts in the BioInert LC like the gold seal(s).
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