How to Read a Certificate of Analysis (COA) for Peptides

Why COAs Matter

When you purchase a peptide, you're trusting that a small vial of white powder contains exactly what the vendor claims. A Certificate of Analysis (COA) is the document that proves — or disproves — that trust.

What a COA Should Include

1. HPLC Purity

What it is: High-Performance Liquid Chromatography measures the percentage of the desired peptide vs impurities.

What to look for: ≥98% purity for research-grade peptides. Below 95% is concerning.

Red flag: No HPLC data, or purity listed without a chromatogram image.

2. Mass Spectrometry (MS)

What it is: Confirms the molecular weight matches the expected peptide.

What to look for: The observed mass should match the theoretical mass within ±1 Da.

Red flag: Mass doesn't match, or MS data is absent.

3. Appearance

Should describe the physical form — typically "white lyophilized powder" for most peptides.

4. Endotoxin Testing (LAL)

Measures bacterial endotoxin contamination. Critical for injectable peptides.

What to look for: <5 EU/mg is standard.

5. Sterility Testing

Confirms no microbial contamination. Not all vendors include this.

How to Verify a COA

1. Check the batch number — It should match your vial
2. Look for third-party testing — In-house COAs are less reliable
3. Verify the testing lab — Google the lab name to confirm it exists
4. Check the date — COA should be recent (within 12 months)
5. Compare across vendors — If vendor A has 99% purity and vendor B has 95% for the same peptide, that tells you something

The Bottom Line

Never purchase peptides from a vendor who can't provide a COA on request. If they hesitate, dodge, or provide a generic document without batch-specific data — find a different vendor.

Your health depends on what's actually in the vial, not what's on the marketing page.