Chromatography Forum

We recently undertook some work to analyse some leachates for non-volatile organics. Not having much experience with this kind of analysis before, we decided that analysis by LC-Q-TOF would be the way to do it, then identifying unknowns by the high-res mass spectra mainly by molecular formula and possible database lookup.

Now, we're exclusively single-quad/triple-quad people here, so Q-TOF is a bit of a dark art to us. We booked some time on an instrument at another organisation. I set up the instrument chromatography identically to how we would a single quad LC-MS, hoping to just get some higher res mass spectra. What resulted was far more peaks in the sample chromatogram than we were anticipating, so now we have to identify them.

One of the problems I'm encountering is how to get reliable interpretations of molecular formula in MassHunter Qual. It seems like there are a whole bunch of ions that are pretty good matches. Is there a way to restrict it to only certain adducts (e.g. only want M+H, M-H, etc.)?

Also, are there good libraries available for general organics, polymer contaminants, etc?

If anyone routinely does environmental or product testing type work with LC-QTOF, I'd been keen to hear how you do it, particular analysing for unknown non-volatile organics.

hi,
I was into LC-MS analysis of extractables & leachables for several years. without any doubt, an LC-qtof is a good choice to start with this kind of analysis. According to my experience, I would strongly advise you to be very careful with the identification of this kind of molecules exclusively on the basis of the molecular formula generated by the software, because you could fail with their correct identification. you shall rather start with the molecular formula generated by the software and ask yourself if that molecule is reasonable for the packaging you are analyzing. moreover, if it is allowed to you, you could also acquire your spectra in a dad-like mode, in order to have a MS/MS for m/z above a certain threshold and to corroborate the tentative identifications you assigned.
Concerning the databases... you could use MzCloud, a very useful database where are reported plenty of MS spectra for a variety of molecules, and you could use PubChem and ChemSpider, which are useful for searching chemical-physical information about the molecules you identified and to search for any hit in the literature.
hope to help you,
Antonio