Chromatography Forum

Hello,

I'm sorry for posting a question which is not related to chromatography at all, but perhaps local MS experts can answer me very easily..

I can see a peak of 256.095 m/z in my cellular extracts. By searching the PubChem database I found this compound - Glycerylphosphorylcholine:
http://pubchem.ncbi.nlm.nih.gov/summary ... ?cid=11234

The compound bears both positive (N+) and negative (O-) charges.
I am using negative ESI ionization.
Is it possible to detect such compounds using negative ESI?
In fact the compound after ionization would have 2 negative charges and 1 positive charge.
I just want to know whether it is possible.

I don't know the compound in question but a couple of questions might help -

a) how accurate is your data, you are quoting 3dp are the rest of your samples/standards coming out at that precision? (is there anything else that would be close to the indicated mass)

b) charge state- what is the isotope seperation of your 256 peak, if it is 0.5da then you have a doubly charged substance of actual mass 512 or so, remembering what you see in a mass spectrum is m/z

ESI creates ions by the addition of H+ in positive mode, and the loss of an existing H+ in negative mode the M+H and M- ions respectively. I assume you have allowed for this in your mass calculations. I am doubtful you would see this compound in ESI-, but the only real way to know is to try some. ESI can be a bit of a black art as to seeing what might theoretically ionise.

The compound has a formula of C8H20NO6P, which after losing one H+ (negative ESI) gives the mass of 296.0955 amu. Our machine's precision is about +/- 0.001 m/z. Charge is 1.

However, I'm not trying to prove whether it is that particular compound or not - it could very well be a different compound with same formula. My question is just whether it is possible to ionize such compounds bearing both charges. I bet somebody has answered this question before...

phospholipids are kind of strange. In the positive ion mode, the singly charged ion would be noted for the phosphorus O groups protonated so it would be neutral and the quaternary amine singly charged ion would be observed.

If you are chromatographing the compound with acetate as the counter ion and acquire the negative ion spectrum, would see a small ion for the compound plus an acetate. The acetate would "neutralize" the positve charge of the ammonium ion and the depronated phosphate group would give you the negative charge. If you up the collision energy on the cone or skimmer or in the collision cell, the acetate would be converted to methyl acetate and thus give you an M-15 ion. Strange isn't it, first saw the M-15 spectrum on the front of the monograph:

Mass Specetometry of Phospholipids: Tables of Molecular and Product Ions by R. Murphy,

I think I have a spectrum of positive ion spectrum of a phospholipid on my web site at http://users.chartertn.net/slittle in the section on matrix effects..