The list of masses appear without charge in my LC-MS chromatogram usig formic acid. I supose molecules did not ionize. What can I do?
I have the feeling that your question is wrong. If the molecules are not ionized (thus without charge) they can't reach the detector and won't be visible in the MS-chromatogram, all manufacturers take extra precautions to avoid non ionized species entering the mass analyzer. Do not forget that the x scale in a ms spectrum is expressed in dalton and not in mass
Hi, Maria -
Can you upload some of your data, and indicate what you're asking about. This would help clarify how to expand on Kris Wolfs' comments.
only charge specie that can go thru Q 1 and Q 3 to see at the detector, The neutral molecule would be pumped out from the instrument. Show me your Q1 tune and what is the molecular weight of your analyte?
Hi Chris and John,
It is true , I did not formulate my question well. The strange thing I observed in the LC-MS analysis of a mixture (electrodegradation products os dibenzothiophene) is that the Q-TOF detector recorded real peaks and I have a good mass spectrum of each peak. However, the table where the equipment presents the m/z values and abundance, did not record a charge. I wonder if I can consider these masses to assign a formula/structure.
I attach a file clarifying what I described in words.
Thanks in advance for your help and advice.
Regards
Maria
Hi, Maria -
Thanks; that helps a lot. There may be a way to change this, but our version of the software only shows the charges if some of the compounds are multiply charged. As a general rule of thumb, compounds with molecular weights less than 500 or 600 daltons rarely have more than one charge (there are of course exceptions). Most of your compounds are well below that so you can be confident that the m/z values are based on one charge.
And remember, you can always double-check the charge state by zooming in on the mass spectra and checking the spacing between the signals in the isotope pattern. If it's 1 dalton, the compound is singly-charged; .5 daltons for doubly-charged, and so on. If you can get a sample, run a set of peptides or a protein digest; that will give you lots of examples.
Regards.
Pete
Hi,
I thank you both for your answers and help. Happy weekend and regards. Maria
Hi Maria,
No doubt that the masses detected in your LCMS must correspond to charged species. The charged species in LCMS are normally in even electron state, but can also be in odd electron. I have analysed numerous highly conjugated molecules and often observed corresponding odd electron ions (molecular ions in terms of GCMS). Your molecules dibenzothiophene and its derivatives are conjugated and they may readily lose an electron under the LCMS conditions to form M+. ions, but you should have also observed other adduct ions. If not, add trace NH4+ or Na+ to the mobile phase to favour their formation.
Cheers,
Y
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