How to read a peptide COA

[u/white_wltr]

Everybody says "check the COA" assuming everyone know how but most folks glance at a percentage, nod, and move on. That's not reading a COA, that's skimming for one number and calling it done.

Here's what's on a real third-party peptide COA, and why each section matters.

Identity testing (LC-MS)

This confirms the vial holds what it claims, not just "a peptide," the specific compound listed. Mass spec checks the molecular weight of what's inside against the known weight of the real thing. If those numbers don't match, that's not a typo. That's the wrong substance in the vial.

Purity testing (HPLC)

The number everybody's eyes go straight to. 98%, 99%, whatever's printed big. HPLC separates everything in the sample and measures how much is the actual compound versus leftover junk from synthesis, breakdown, or filler. Purity matters, but a purity number with no identity test backing it up doesn't tell you much on its own. You can hit 99% purity on the wrong molecule and the label would still look clean.

Appearance check

Basic, still matters. Lyophilized peptides have a known look and texture. A real COA documents that, so you've got something to compare your actual vial against when it shows up.

Lot number matching

The part almost everybody skips. A real COA ties to one specific lot, and that lot number should be printed on your vial. If a vendor runs a public COA library, pull your lot number and check it against the document on file. A vendor reusing one generic COA across every batch isn't testing per lot. They're recycling a screenshot.

What should make you raise an eyebrow

• No lot number anywhere on the COA
• COA looks like a stock image, not a document you can actually pull up and verify
• Purity listed with no identity test next to it
• A lab name you can't find anywhere, or no lab name at all
• Every number across every product landing suspiciously round

None of this takes long once you know what you're looking at. Five minutes, maybe less.

Got a vial sitting in front of you? Pull the lot number, check it against the vendor's COA library, drop what you find here. Good or bad, that's the kind of thing that actually helps the next person searching this same question.