Distinguishing a deletion sequence by mass alone

Taking post #18 at face value and following it one step further.

Sample preparation for mass spectrometry can itself introduce modifications, particularly oxidation. A finding at trace level may be telling you about the preparation rather than the material.

The general case is well covered; this is the awkward specific one.

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.

Flagging that the sources on this are thinner than the confidence in the thread suggests.

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.

I have kept the units in throughout, for the obvious reason.

That is a fair summary of where the discussion has got to.

Monoisotopic and average mass are different numbers and both appear on documents. At this molecular weight the difference is a few daltons, which is more than the tolerance being claimed.

Stating my assumptions rather than smuggling them in.

Sample preparation for mass spectrometry can itself introduce modifications, particularly oxidation. A finding at trace level may be telling you about the preparation rather than the material.

Same conclusion as the reply above, reached differently, which is mildly reassuring.

Adducts — sodium and potassium especially — shift the observed mass in predictable increments. A report showing an unexplained plus twenty-two is usually showing you a sodium adduct.

This is the version I would want a new member to read first.

I have been on both sides of the distinguishing a deletion sequence argument in this category within eighteen months, which should tell you how strong the evidence for either side is.