m/z value lcms

[joey99]

hi
i have done lcms -it-tof assay, for a meoh fraction of a plant extract

the plant has many other related tribe somewhat

Polygonum spp...

One paper described analysis of 4 different Polygonum species, and identified a number of compunds, and published the m/z values

Now, my polygonum species is not listed in their paper, but my lcms it tof output detected a number of compounds with similar
m/z values (plus and minus ion modes)

could i just cite the m/z values they published to claim that my compounds are as what they found.. i didnt have the resource at the moment, to get the standards and run hplc to conclusively say the compounds im trying to imply

TIA

[lmh]

It's a difficult one, but a lot depends on where you are publishing. If your plant is closely related to the other 4 species (highly likely) then it is highly likely it will share many of the same biochemical pathways and make the same products. If you are publishing in a physiological journal, not a phytochemical one, and the identity of the peaks is a nice extra in your paper rather than the central feature of the argument, then you may well be able to publish with the data you have, provided you don't try to over-interpret. A more chemically-orientated journal would require a much better standard of proof.

My approach would be to cite the other paper copiously, and indicate that your data suggest your species is similar to the existing 4 species, producing similar products (I wouldn't claim identical, just in case of isomers etc.); you can back this up with accurate mass (an IT-ToF has probably given you data to within 5ppm?), and if you had UV detection, don't forget to check whether you have similar UV maxima, which are another diagnostic feature. If you have MS^n data, it is also worth checking whether these generally agree with the expected structures.

In the end it depends on the reviewers, but given that many phytochemicals are almost impossible to source as standards, and some are nearly impossible to purify in sufficient quantity for NMR, your situation isn't unusual. I think many of us appreciate that there is a dilemma, and that sometimes it is better to accept a lower standard of evidence than block publication of papers that otherwise make a useful contribution to general knowledge.

[carlo.annaratone]

I am in a situation similar to yours. I am working on a plant of the asteraceae family whose sesquiterpenes have already been characterized in the past with MS and NMR, but do not have available standards. I cannot perform purification, therefore I must rely on LC-Q-TOF.

I gathered all the data I could get from the MS accurate mass mode (+/- 5 ppm):

Quasimolecular ion in positive and negative mode (including adducts with chloride and sodium etc...)
tandem MS for positive and negative ion (some fragments were described in literature, other could be logically matched with the structures)