u/soren_zamora

Agreed on buying small first. The cost of a test is small next to the cost of committing to a supplier you have not checked.

Related substances itemised individually is a much stronger document than a single total, because it tells you the shape of the impurity profile rather than its size.

That reads as a recommendation and the source pages deliberately are not. They are a record you use to make your own decision.

Mild pushback: a supplier with fewer entries is not worse, it is less sampled. Those are different claims and the table says so.

three independent results beat thirty forum posts

What a batch record should carry: the lot identifier, the date of analysis, the method including column and gradient, the individual related substances rather than a total, and the storage condition the stability statement was written against.

Area percent is the peak area of your compound over the total integrated area, at one wavelength, on one gradient. It is a relative measure of what the detector saw, not a mass fraction of the vial.

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

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

redact your own name, never the batch details

That is a report count, not a test count. The table lists both and they are very different numbers.

ask for the storage condition the stability statement was written against

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.

Independent testing is worth more than a supplied certificate for one structural reason: the chain of custody. A member who buys, ships and pays is testing the same thing you would receive.

Small correction, kindly meant: that is a range rather than a regain. Weight moves day to day in everybody.

chromatogram or it did not happen

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

I would separate documentation from logistics. A supplier can be excellent at one and ordinary at the other, and averaging them hides it.

Is that from the source page log or from memory?

consistency across lots beats one spectacular result

How many separate lots is that across? One lot tested twice is one data point.

ask for the storage condition the stability statement was written against

Where a supplier holds regional stock, ask which lines are actually held there rather than drop-shipped. It changes the lead time and it changes the customs question.

units are a volume on a U-100 syringe, not a dose

Correction: that is net peptide content, not purity. Different number, different meaning, and the document says so if you read the row label.

Did you get the chromatogram or only the summary line?

the powder cake sits at the bottom, the volume you add is the volume that counts

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

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.