Reconciling a label claim with a content assay

On the subject in the title: Reconciling a label claim with a content assay Working notes rather than a conclusion.

The question about reconciling a label claim that I actually want answered is the second one below. The first is context and I have kept it short.

Both are stated with units, and I have said what I already checked so that nobody repeats it.

Reading back through, this was answered upthread and I missed it. My fault.

Water content (residual moisture) matters: lyophilised peptide is not dry. A few percent water is normal. The difference between a TFA salt and an acetate salt can be several percent. Content calculations need the water content to be accurate.

Purity and content are different measurements: purity tells you what proportion of the detected material is the intended species. Content tells you how much of the intended species is present in the container. A lyophilised vial can be 99% pure and contain considerably less than the label claims because the remainder is water, counter-ion and excipient.

Peptide content and chromatographic purity are separate determinations and a certificate that reports only one has answered only one question. Content is the one that tells you how much is in the vial.

I read post #4 twice before replying, because I had assumed the opposite.

Amino acid analysis gives content: it hydrolyses the peptide and quantifies the residues. It measures the peptide content independent of chromatographic purity. Very few supplier certificates report it.

Stating my assumptions rather than smuggling them in.

Purity and content are different measurements: purity tells you what proportion of the detected material is the intended species. Content tells you how much of the intended species is present in the container. A lyophilised vial can be 99% pure and contain considerably less than the label claims because the remainder is water, counter-ion and excipient.

The right answer here may simply be that it has not been measured.