This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1.
Quantitation by MS: most quantitation is done by LC-UV detection at 214 nm, not by MS, because extinction coefficients are better known. MS can quantify if an internal standard is used but that requires preparation.
Positional isomers and epimers are mass-identical. Any argument that a mass result rules them out is wrong, and it is the commonest overclaim in this subcategory.
That much is documented. The rest is how I have interpreted it.
That is consistent with mine, for whatever one more account is worth.
Post #31 is the version of this I will quote in future. One addition.
Resolution and mass accuracy are different specifications. An instrument can resolve two species and still assign their masses imprecisely, and the reverse is also possible.
The conclusion is tentative; the arithmetic underneath it is not.
The honest summary of what a mass result buys you: it narrows the field of what the material could be, considerably. It never closes it, and no certificate should be read as though it had.
Nothing above should be read as advice about what anyone else should do.
Picking up post #35: that is the part I would want checked first.
Tandem mass spectrometry with fragmentation gives sequence information that intact mass cannot. It is the analysis that would actually confirm identity, and it is rarely supplied.
That is all I can say without guessing.
I had written a reply contradicting post #35 and deleted it. Here is what survived.
Resolution: "high resolution" commonly means <5 ppm across the mass range. Unit-resolution instruments achieve ±1 Da at best and cannot distinguish two species differing by less than 1 Da in total mass.
Worth separating two things that post #35 runs together.
Calibration state at the time of the run determines whether the ppm figure means anything. A report that states when the instrument was last calibrated is unusual and is worth more than one that does not.
That is what the documentation says. What happens in practice is usually close.
Thank you for the correction. I would rather find out here than later.
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