Chromatography Forum

I know that TOF isn't used widely in forensic analysis. But we are using it.

Any opinions on this matter? What much more do you need to confirm the identity of a substance...

Exact Mass within 5 ppm. Retention Time. Possible spectral matching, by in-source CID.

Can anyone argue with that?

I believe RIVM did a study comparing multi-ion QQQ confirmation with exact mass TOF confirmation across a variety of analytes, determining both false positive and false negative rates by fortified sample analysis. Can't seem to find actual reference, though, so I may be misremembering details (or even the entire study ':?')

Here's an interesting reference on the topic, with recommendations for changes to EU criteria:
Analytica Chimica Acta
Volume 586, Issues 1-2, 14 March 2007, Pages 122-129

I think you need at least two qualifying ions for a confirmation. I don't know a lot about TOF but on a LC/QQQ you cannot tell the difference between Pentobarbital and Amobarbital. They have the same MW and product ions. Same retention time. It takes a full spectrum to tell them apart. Better with derivatization. I'm sure there must be other examples.

Mike

If you just want to identify a compound (and you already know something about it), TOF will work great. The differences with a QQQ will be in the LOD. Also the TOF have limited dymanic range so you probably will be limited to 3 orders of magnitude (you are going to loose mass accuracy for the most abundant compounds if you inject too much).

Finally, in terms of metabonomics where you do not know anything about your compounds and you need to identify them, TOF by itself is not enough (and as you did not specify an application I can mention it). There are in silico calculations describing how far you can go with a TOF depending on the MW of the analyte, assumptions on elements etc...