TIC of LC/MS versus GC/MS

[jameslizh]

Total ion chromatography (TIC) from LC/MS and GC/MS is quite different. GC/MS one shows very nice peaks. But LC/MS one in most cases is not and without using extracted ion chromatography (EIC) or some data mining tool it is very tough to see the peak (compounds) visually. In principle, why is that? simply because of ionization difference and/or solvent (mobile phase) effect?

[sepscientologist]

Hmmm... I'm not sure but perhaps because the LC TIC has a large contribution from solvent/buffer
while by GCMS the mobile phase does not contribute appreciably to the TIC. The GCMS TIC
is all eluting compounds.

[Karen01]

Total ion chromatography (TIC) from LC/MS and GC/MS is quite different. GC/MS one shows very nice peaks. But LC/MS one in most cases is not and without using extracted ion chromatography (EIC) or some data mining tool it is very tough to see the peak (compounds) visually.

That is certainly NOT wat i saw today... I got TIC peaks that very much mirrored what I saw from a UV max Plot from a PDA (as well as some others)... the TIC peaks were easily recognized as peaks.

- Karen

[Klaus I.]

Total ion chromatography (TIC) from LC/MS and GC/MS is quite different. GC/MS one shows very nice peaks. But LC/MS one in most cases is not and without using extracted ion chromatography (EIC) or some data mining tool it is very tough to see the peak (compounds) visually. In principle, why is that? simply because of ionization difference and/or solvent (mobile phase) effect?

Yes, I think both things have an effect on the TIC. In GC/MS with EI-ionization you have not much noise from the mobile phase e.g. 99.999% helium. With LC/MS and ESI-ionization you have a bigger volume of mobile phase which have also not this quality like helium (even when you use lc/ms grade solvents and buffer substances).

Nevertheless if your substance is good ionizable or a permanent ion, you get also a nice peaks in your TIC. It depends on you application but it is not uncommen to see no peaks in your TIC. Therfore you can use a background substraction function of your software or a second detector eg. UV-detector.

Regards
Klaus

[lmh]

base peak chromatograms are often worth looking at in LC-ESI-MS, if your software does them

[Maestro]

Hello) All chemist know, that in gc/ms we can use DATA Mass-Spectral for identification our component (NIST, Willey and etc.) . I want ask you, LC/MS/MS/MS have similar method for idetification compounds, without RM. Sorry of my English. )))))

[lmh]

Masetro, you might do better to ask your question again in a new thread. My answer is that spectral libraries for LC-MS are appearing (for example in Metlin, Scripps institute), but are very poorly developed compared to NIST etc., and are harder to use because different LC-MS instruments produce different MS2 spectra from the same compound. I am not, however, a great expert in the field!

[Maestro]

Thank you. I am very glad, that in chemistry world mass spectral data base for LC-MS is exist. I saw (http://www.massbank.jp/QuickSearch.html) LC-MS parameters and equipment in properties for mass spectral search. After that i'll want to order for my laboratory LC-MSn, because need analysis nonvolatile compound. But i haven't RM.
sorry for my english, the best regards. After several weak i'll, may be, create new topic, after i'll accumulate more information about this theme.

[thohry]

I realize that if I run a MRM method with different precursor ions and of different fragmentors..., the online TIC chromatogram looks very bad while in the data analysis, it looks normal.