C15H17O6N3-Calculated Exact Mass: 12.0000 (15C) + 1.0078 (17H) + 14.0031 (3N) + 15.9949 (6O) =335.30925.
According to the Nitrogen Rule, the chemical structure contains an odd number of nitrogen atoms (3N), indicating an odd nominal mass. So [M+H]+, [M-H]- the molecular ion peak should be an even number. Under negative ESI mode, 334 maybe the [M-H]-.
Also under Positive ESI Mode, there are peaks of 336[M+H]+， 358[M+Na]+，371[M+K]+. So the conclusion is 339 could not be [M-H]-.
In practical of NegESI, it is difficult to explain the molecualr ion is the peak of 339: How could it disassociate a Fragments ion of 5 to obtain a Fragments ion of 334. Also, please double check the Mass Spectrum of Positive ESI, there is not Fragments ion of 341. Also confirm that the irrational of molecular ion of 339.As for the fragment peak of 339, that maybe is from the system contamination or the impurity in the analyte. That is the reason why I asked you obtain a positive ESI Mass@ Friday.
