[bryanh]

Hi

I've been doing some ESI MS on dAMP which is negatively charged. My own data and the literature shows that protonated dAMP has a single positive charge (iget a peak at 332; the MW of dAMP is 331). Surely it should be neutral? Can anyone explain this?

[xanthocyanopia]

Is there a peak at 331 in addition to 332?

[bryanh]

Thanks for the reply
No there isnt, there is a major peak at 332 and smaller ones at 333 and 334 which correspond exactly to the expected isotope pattern.  

[bryanh]

i think ive sorted the problem. I think my source for the mass was wrong. they showed the unprotonated formula and then gave the mass of the protonated form.

[xanthocyanopia]

What is your solvent?  Im assuming that the instrument has been calibrated right?

[bryanh]

my samples are aqueous, but i'm not sure what the solvent system is in the mass spec or its calibration, i would need to check with the tech who runs it. But i dont think either of thse would be the problem. I think the molecule when uncharged (protonated) has a mass of 331, so a mass of 332 and a single positive charge (another proton) makes perfect sense now.

[bryanh]

Hi i've got another question related to this, with various salts added i get peaks corresponding to dAMP+metal, dAMP+metal+nonmetal, I have been trying to find out if this species could be formed in vitro or are they more likely to be formed in the gas phase in the electrospray.