[2026 update] Charge states for a 4 kDa peptide, worked through

This follows post #11 rather than contradicting it.

The arithmetic for a doubly charged species is (M + 2 x 1.00728) / 2, and the analogous expression for higher charge states. Working it through once makes the reported values legible.

That is the version I use. It may not be the version that is correct.

Charge states would be much easier to settle if anyone reported the denominator. Almost nobody reports the denominator.

Something worth flagging about Charge states: the strongest-sounding claims in this thread are the ones with no source attached, which is the usual pattern and not a coincidence.

This follows post #51 rather than contradicting it.

What I want from this Charge states thread is the list of things that would need to be true for the claim to hold. If we can write that list, we can check it.

Noted, and I have changed what I was going to do on the strength of it.

Electrospray ionisation produces multiply charged ions. For a 4 kDa peptide you expect mostly 2+, 3+, and 4+ charge states. Reading an electrospray spectrum means recognizing the envelope, not looking for one peak.

Post #96 answers the question as asked. The question underneath it is different.

Having read the whole Charge states thread before replying: the question in the first post has not actually been answered yet, and three of us have answered a nearby one instead.

Post #116 put the caveat in the right place and I want to underline it.

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.

Anyone who has looked at this more carefully, please correct the record.

Post #125 put the caveat in the right place and I want to underline it.

Trifluoroacetate adducts are common in material purified with TFA and are one reason a mass spectrum from a peptide can look busier than expected.