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 lot number on the COA should match the vial you received. A generic COA reused across batches is a red flag.

2. Look at the HPLC chromatogram, not just the percentage. You want one dominant peak with a clean baseline. Lots of small peaks or a shoulder on the main peak suggest 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 reports carry more weight than in-house ones. Check that the lab name, date, and report details are traceable.

5. Purity vs. net peptide content. 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.

Storage matters too. Lyophilized peptides are much more stable than reconstituted ones, and a good COA doesn’t help if the cold chain failed in shipping.

All of this applies to research-grade material for lab use only. 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 information if you want a visual reference, but the checklist above works for any supplier’s report.

What other red flags have you seen on COAs?