I have a compounds 2'-Deoxyguanosine monohydrate, C10H13N5O4.H2O, with monoisotopic Mass of 285.1073, I wonder if it has the same mass spectrum with 2'-Deoxyguanosine (267.0968)?
I trust you are using electrospray ionization technique so you should observe the molecular ion at [M+1]+ which is 286 for the 2'-Deoxyguanosine monohydrate and 268 for the 2'-Deoxyguanosine.
Yes, I am using ESI-Q-TOF-MS, I show you the obtained mass spectrum of 2'-Deoxyguanosine monohydrate (285.1073). In the spectrum, it doesn't has [285.1073+H] or [285.1073+Na]. However, it has [267.0968+H], [267.0968+Na], [267.0968+K] and [2×267.0968+Na]. it seems that this compound has same spectrum with 2'-Deoxyguanosine.
I'd be cautious in interpreting any differences. Hydration can be observed in ESI as a result of the ionization:
Article Hydration of Gas-Phase Ions Formed by Electrospray Ionization
In contrast, collisional desolvation in the atmospheric pressure interface can strip off water of hydration. The API conditions are a very important parameter. I'm not an NMR expert, but I'd guess that NMR would be a better way to characterize hydration.