[Nescafe]

Hi,

I boc protected an amine group and on the other end is an alcohol, I thought in the mass spec my boc would fall off but it did not but instead I see my M+ with two sodium. So my peak + 46, is it possible for this to occur? I have not experienced this before (and been doing it a long time)

Nescafe.

[ziqquratu]

I apologise if you already know this, but you must always recall that the peaks you see in a mass spectrum are not mass - they are mass/charge (m/z) ratio. Assume your mass is 100; for [M + Na]⁺, m/z is 123/1 = 123. For [M + 2Na]²⁺, however, m/z is 146/2 = 73.  Therefore, if you have a peak at 146, it must not be [M + 2Na]²⁺.

It could be some species other than Na⁺ is providing the charge, or it could be you've got some other neutral species in there as well - EtOH, for example, has a mass of 46 and could easily form part of the charged complex if it were used as the solvent. Or perhaps some combination of a neutral and a charged species (eg. [M + MeOH + Na]⁺ would give M+55 - too high, I know, but it is a common example and I cant think of one off the top of my head that gives M+46!)

[Nescafe]

Thanks for the reply.

Well explained. Thing is, with an alcohol I assumed the overall charge would still be +1 not +2. Basically let us say I have  R-OH. I assumed the possibility of having R-O^{- +}Na + ⁺Na So for clarity formula would be RO^{- +}Na₂. I think it is unlikely but sometimes when you are chasing a molecule you fabricate all scenarios possible so it makes sense

[phth]

Also, looking at the isotope peak Δm/z will tell you what charge it has.