Peptide Critic Community

Disclosure first: I work for Peptriva Research (research-use-only compounds), and I can't help with anything use-related. Testing questions are fair game though.

The way I explain this to people: mass spec and HPLC are answering two different questions, and vendors love to blur them together.

LC-MS tells you whether the molecule is what the label claims. It matches the molecular weight against the expected sequence, and that's it. A passing mass spec says nothing about how much of the vial is actually that molecule.

The purity % everyone quotes comes from HPLC, which is basically asking how much of the chromatogram is the main peak. Thing is, stuff like endotoxin doesn't show up there at all, which is why a decent COA lists LAL and microbial as separate tests instead of hiding behind one purity number.

So if a COA only shows one of these, you're getting half an answer. You want identity, purity, the contaminant screens, and a lot number that matches your vial. If you've got a specific COA you're squinting at, post it or DM me and I'll walk through it.

Full disclosure, I work for Peptriva (research-use-only compounds), so factor that in. Can't help with anything use-related but COA stuff is basically my whole job, so.

Honestly you kind of answered your own question. If you have to go hunting or email a vendor to get a COA, that tells you most of what you need to know. Vendors doing it right just put it on the product page, per batch.

If they do send you one, look for the lot number first. No lot number means it's a generic doc they could be reusing across everything. Then check it actually names the methods, LC-MS for identity and HPLC for the purity number. Endotoxin and microbial should show up as their own line items too, the purity % doesn't cover those. One thing people miss: if every product on a site comes back exactly 99.9%, that's worse than seeing a bit of spread. Real results vary.

And after the whole Paradigm thing, worth remembering a vendor's own COA can just be made up. The only thing that actually settles it is independent testing, either an ISO 17025 lab or customer-submitted Janoshik results. Same standard applies to us, for what it's worth.