u/ignacio_silva

Net peptide content is the fraction of the powder that is actually peptide once counterion, water and residual solvent are accounted for. A 99% pure acetate salt can still be about 85% peptide by mass.

a prescription from one member state is not automatically valid in another

what does the certificate actually carry — that is the whole question

Agreed — the itemised related substances table is the difference between a document and a receipt.

Adding the bit that always gets missed: the lot on the vial has to match the lot on the page, or none of this applies to your material.

Batch number and date of analysis, are both on there?

Yes. Spread across lots is the number that tells you about the process. A single high result tells you about a vial.

a total of 0.4% tells you less than four named impurities adding to 0.6%

This. Ask for the batch record. The ones who send it inside a day have told you more than any review could.

Correction: that supplier is in the documented twenty with a source page, not in the wider-market table. Different evidence bases entirely.

UV at 214nm sees the peptide bond and picks up almost everything; at 280nm you are looking at aromatics only. Which wavelength the number came from is part of the number.

Right — BCH publishes the method line on the certificate, and once you have seen one that does you notice every one that does not.

Small fix — the figure you quoted is the claimed purity from the certificate, and the independent result was the higher of the two.

Area percent or net peptide content? They answer different questions.