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December 12, 2014 at 7:52 pm

Corante Blogger: ‘NMR of a Mass Spec Species’

Blogger Derek Lowe writes about a journal article on “Nuclear Magnetic Resonance Structure Elucidation of Peptide b2 Ions” by Ohio University researchers Pengyuan Liu and Dr. Hao Chen of the Center for Intelligent Chemical Instrumentation, the Department of Chemistry and Biochemistry, and the Edison Institute of Biotechnology at Ohio University.

I have to say, I didn’t even know that this could be done. This paper from Angewandte Chemie describes a mass spec/NMR combination analysis that had never occurred to me as possible. The authors (from Ohio U. and Purdue) are looking at a common peptide ion seen in proteomic mass spec studies. And what they do is collect enough of the ions to run an NMR. That just seems bizarre, somehow, because I think that most of us picture the ionic fragments in a mass spec as these ghostly, esoteric things that live only in the outer-space-like vacuum of the instrument (and are present in vanishingly small amounts, at that). The idea of piling them up and running their NMR spectrum seems like someone taking a reflectance IR spectrum of an angel’s wing.

That’s because NMR, for most organic chemists, is a much more home-style, hands-on technique. We take measurable amounts of compounds, stick them into glass tubes, and use pipets to dissolve them up in solvent before taking them over to the NMR instrument. You get your hands on these things – and if you need to, you can go get the tube after it comes back out of the magnet, evaporate the solvent, and get all your sample back. Mass spec, on the other hand, uses ridiculously tiny amounts of material. It’s really, really hard as an organic chemist to underload an LC/MS – it seems like you’ll always get something, if there’s something to get. You take a spec of sample, dissolve it in solvent, and then the machine takes a sip of it that a mosquito wouldn’t bother with, because it doesn’t need the rest.

Read the rest of his post.

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