How to actually read a peptide COA (what to check beyond the purity number)

A lot of people see “99% purity” on a COA and stop there. That number alone doesn’t tell you much. Here’s what I check first:

1. Is it batch-specific? The COA should carry a lot/batch number that matches the vial you received. A generic COA reused across batches is a red flag.

2. HPLC chromatogram, not just a percentage. Look at the actual trace. You want one dominant peak with a clean baseline. Lots of small peaks, or a peak shoulder, suggests impurities even if the summary says 98%+.

3. Mass spec confirmation. HPLC tells you how pure the sample is, not that it’s the right compound. MS confirms the molecular weight matches the expected peptide. A COA with HPLC but no MS is only half the picture.

4. Who ran the test. Third-party lab results carry more weight than in-house ones. Check that the lab name, date, and report details are real and traceable, and that the file hasn’t obviously been edited.

5. Content vs. purity. Purity is the percentage of the target peptide among peptide-related material. Net peptide content (how much of the powder is actually peptide vs. salts and water) is a separate number, and many COAs skip it.

I’d also pay attention to storage and handling, since lyophilized peptides are much more stable than reconstituted ones, and a COA doesn’t help if the cold chain failed in shipping.

Standard caveat: all of this applies to research-grade material for lab use. I can’t speak to human use, and many of these compounds aren’t approved for it.

Disclosure: I’m affiliated with Patriot Peptides. We put together this COA breakdown with example chromatograms if you want a visual reference, but the checklist above works on any supplier’s report.

Curious what other red flags people here have run into on COAs.