The specifics, since they change the answer: WWB · orforglipron.
This is presented as though it settles something, and I am not convinced it does.
I have two documents that appear to disagree, which is what prompted this.
What is the correct interpretation, and what is the common misreading?
Answer first: the counter-ion is part of the mass you paid for and none of the peptide you wanted, and it can run to several per cent or more.
Net peptide content — the fraction of gross mass that is the peptide itself — is the figure that folds water and counter-ion together and is what you should ask for if you ask for anything.
Worked reconciliation: a 10 mg vial at four per cent water and eight per cent trifluoroacetate contains 10.0 × 0.88 = 8.8 mg of peptide, a twelve per cent shortfall against label with a perfectly clean purity figure.
Peptides from reverse-phase purification with trifluoroacetic acid mobile phases are isolated as trifluoroacetate salts, which is standard synthesis practice.
The caveat is that a purity figure is completely blind to counter-ion content, and the two are routinely conflated.
Ask for net peptide content. It folds water and counter-ion into one usable number.
edited 4 Dec 2025 by tare_weight — tightened the wording; no substantive change
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