Records where adducts (ION) are numbers, not [M+H+]+, etc
Sometimes, the GNPS records have the following form:
BEGIN IONS
TITLE=mzspec:MSV000082891:20170406_10431116_Metabolomics_Sample31.mzML:scan:7917
PEPMASS=195.13821679884
CHARGE=0+
ORIG_COMPOUND=N-Dodecanoyl-DL-homoserine lactone
ORIG_INCHI=InChI=1S/C16H29NO3/c1-2-3-4-5-6-7-8-9-10-11-15(18)17-14-12-13-20-16(14)19/h14H,2-13H2,1H3,(H,17,18)
ORIG_INCHIKEY=WILLZMOKUUPJSL-UHFFFAOYSA-N
PREDICTED_FORMULA=nan
MZ_DELTA=12.036
MZ_DELTA_EXPLANATION=Ser->Val substitution|Thr->Leu/Ile substitution
MZ_DELTA_ATOMIC_DIFFERENCE=2C,4H,-1O|2C,4H,-1O
ION=[183.1]
SCANS=46815
MSLEVEL=2
54.45156478881836 1444.301025390625
55.01865768432617 1717.0672607421875
55.0551643371582 6298.52490234375
57.03435134887695 1863.9461669921875
57.07073974609375 3707.934814453125
67.05503845214844 8756.353515625
67.6009292602539 1542.152587890625
69.03437042236328 1832.8424072265625
69.07084655761719 11730.3388671875
71.04988861083984 6715.04541015625
79.05494689941406 12181.3740234375
81.07056427001953 14299.345703125
...
This is clearly not the standard adduct form. Also, the charge is 0+
(Maybe M+ ?).
...
ION=[183.1]
...
I have trouble interpreting this. Normally, the record's PEPMASS
entry contains the parent ion mass and if you substract, or add DELTA_MZ
value to this number, you get the mass of the ORIG_COMPOUND
. I know this, because I checked it using the wonderful resource called PubChem.
However, for the record above, DELTA_MZ is the difference between the mass in the ION
entry and PEPMASS
. Of course, if this is some kind of process where a neutral compound breaks up into fragments "directly", then ION
entry can be ignored. It's just that these kind of numerical peculiarities draw my attention so I wanted to double check.