How to Read and Verify Peptide Testing Certificates (COAs)

What "pure peptides" really means

When a supplier advertises "pure peptides" or "certified peptides," what should you actually look for? Purity is a measurable property — the percentage of the labeled peptide in the lyophilized powder, measured by reverse-phase High-Performance Liquid Chromatography (HPLC). Research-grade peptides are typically ≥98% pure. Anything that doesn't ship with a batch-specific third-party report is unverified, regardless of marketing claims.

What a Certificate of Analysis (COA) contains

• Batch / lot number — must match the label on your vial.
• HPLC purity — chromatogram with a clean main peak and the % area integration.
• Mass spectrometry (MS) — confirms the molecular weight matches the target peptide's theoretical mass.
• Endotoxin (LAL test) — for any peptide intended for injection research, endotoxin should be below standard pharmacopeia limits.
• Sterility / appearance / solubility — basic physical QC.
• Testing lab name, date, signature — the report should come from an independent lab, not the supplier's own bench.

How to read an HPLC chromatogram

The chromatogram is the chart on most COAs. The main peak should be tall, narrow, and well-separated from smaller peaks. The integration table reports the % area of each peak — the main peak's % area is the reported purity. Be skeptical of reports where the main peak is broad, where there are several large secondary peaks, or where the integration table is missing.

A 6-step verification checklist

1. Find the COA on the supplier's product page — not a generic one.
2. Match the batch / lot number on the COA to the number printed on your vial.
3. Confirm the testing lab is independent (named, with contact info or a website).
4. Check HPLC purity ≥ 98% with a clean dominant peak.
5. Confirm the mass-spec measured mass matches the peptide's theoretical mass within ~1 Da.
6. For injectable research, verify endotoxin is below the published limit on the report.

Red flags

• One generic COA reused across every product.
• No batch / lot number, or one that doesn't match the vial.
• Testing done in-house with no independent lab named.
• Purity claims without a chromatogram.
• Missing mass-spec identity confirmation.