Metabolite identification

August 08, 2011, 01:52:57 PM

Hello,

I was wondering what the acceptable +/- ppm window is when identifying a compound? I am obtaining accurate mass data with an LC-ESI-TOF-MS and I know XCMS searches metlin within 0.15. Just wanted to get the general opinion before I start searching other databases-
Thank you!

Ashley

Re: Metabolite identification

Reply #1 – August 08, 2011, 02:33:23 PM

The ppm window depends on your instrument accuray. For a TOF, 10-30 ppm would be normal.

However, the result of a database search by exact mass should only be considered a putative ID.
Even with 0 ppm mass deviation, the correct ID has to be verified by MS/MS and retention time of a standard.

e.g., a METLIN search for m/z 181.0707, [M+H]+ only, will result in 19 hits with 0 ppm.