Chromatography Forum

Hello everyone,

I have a compound with a molecular weight of 309.1. When I infused/optimized the compound in positive mode electrospray on my MS with and without flow, I'm seeing large responses at 309.1 and 311.1, and a small response at the predicted 310.1. I could not get a signal in ESI negative mode, or APCI.

All three parents have the exact same product ion scan, so I'm assuming they're all related to the compound I recieved.

I've seen compounds lose functional groups, ionize with odd adducts, but I've never seen a response that's 1 unit above and below. I've also seen deuterated compounds that were not completely pure show similar scans, but this compound is not deuterated. I only have the molecular weight of the compound, no structure was given.

Sounds like you have a chlorinated compound. A single chlorine will give you that exact pattern and the mass after loss of the chlorine will be the same for both chlorine isomers. Does the lower mass have a slightly higher response than the higher mass?

further to what James wrote: if by molecular weight of 309 you mean that's the molecular weight printed on the bottle, or the weight given as "Mol. Wt." as opposed to "Exact Mass" in ChemDraw, then it is the average mass of all the isotopomers (weighted by their abundance; in effect, it tells you how much stuff to take, given the natural mix of isotopes, to make a 1 Molar solution). If you've either got a compound with a couple of chlorines, or one bromine, then in fact it will have two main isotope peaks present, one at 308 and one at 310, so its average mass is 309, but the mass spec will see the two isotope peaks separately, both + adduct, so you'll get 309 and 311.

That makes sense, forgot that the molecule could be chlorinated, it's been awhile since I've worked with a chlorinated molecule.
Thanks for the responses.

Is it known whether compound has N ?