Why a certificate has to be lot-specific, not product-specific

Every manufacturing run of a peptide is its own batch, with its own synthesis conditions, purification pass and final testing. A product spec sheet describes what a compound is supposed to be; a certificate of analysis describes what one specific manufacturing run actually measured. The two are not interchangeable, and a supplier that only offers the first is only telling you the design intent, not the result.

This is why every certificate carries a lot number, and why that lot number is printed on the vial label rather than buried in paperwork. If the lot number on your vial doesn't match the lot number on the certificate you were sent, the certificate describes a different manufacturing run — it may be accurate for that run and still tell you nothing about the vial in front of you.

Run-to-run variation is normal in peptide synthesis, not a sign of a problem: small differences in purity, trace related substances, or exact fill weight are expected between batches even from the same manufacturer and process. The point of lot-specific testing isn't to catch failures, it's to give you the actual figures for the material you're using, rather than an average or a target.

When requesting a certificate, the two things worth confirming are the lot number match and the presence of both purity (RP-HPLC) and identity (ESI-MS) results with their methods stated — see our guide to reading a certificate of analysis for what each of those numbers means. We release a certificate for every lot we sell, and send the certificate matching your vial's printed lot number the same day it's requested.