How to Read a Peptide Certificate of Analysis (COA)

A Certificate of Analysis (COA) is the document that proves what's actually in a peptide vial. A meaningful COA reports two things for a specific lot: identity (confirmed by mass spectrometry) and purity (measured by HPLC, shown as a percentage) — with a lot number you can match to the vial in your hand. Learning to read one is the single best skill for judging a research peptide, because "grade" describes a standard while the COA describes the actual material.

Here's how to read each section — and how to tell a real, lot-matched COA from a generic PDF reused across batches.

Why the COA Is the Whole Ballgame

Every vendor claims high purity. The COA is what turns a claim into something verifiable — but only if it's tied to your specific lot and, ideally, produced by an independent lab. Without a lot-matched COA, a purity number is just marketing.

The Two Numbers That Matter Most

• Identity (mass spectrometry): confirms the molecule is what the label says by matching its measured mass to the expected mass of the peptide. This answers "is it the right compound?"
• Purity (HPLC): separates the sample into its components and reports the percentage that is the target peptide — commonly ≥98% for quality research material. This answers "how much of it is the real thing versus impurities?"

Identity without purity, or purity without identity, only tells half the story. A good COA has both.

Reading the Rest of the COA

• Lot / batch number: must match the number printed on your vial. This is the link between the paper and the product.
• Test date and method: shows when and how it was tested (e.g., HPLC conditions, MS method).
• Appearance and other specs: physical description, sometimes water content or net peptide content.
• Testing lab: independent third-party testing carries more weight than in-house-only results.

How to Spot a COA That Actually Means Something

• The lot number on the COA matches the vial — this is the number-one check.
• It reports both HPLC purity and mass-spec identity, not just one.
• The HPLC chromatogram is included (a clean main peak), not just a bare number.
• It's specific to a batch, not a generic PDF you suspect is reused across every product.
• Bonus: an independent lab name and contact.

If a "COA" is a generic sheet with no lot number, no chromatogram, and a suspiciously round number reused everywhere — treat the purity claim as unverified.

Frequently Asked Questions

What is a Certificate of Analysis (COA)?

A COA is a lab document that reports what a specific lot of peptide actually contains — its identity confirmed by mass spectrometry and its purity measured by HPLC — tied to a lot number you can match to your vial. It's the primary basis for trusting a research peptide.

What should a good peptide COA include?

At minimum: HPLC purity (a percentage), mass-spec identity, a lot/batch number that matches your vial, the test date and method, and ideally a chromatogram and an independent testing lab. Both purity and identity should be present — one without the other is incomplete.

What does HPLC purity mean on a COA?

HPLC (high-performance liquid chromatography) separates a sample into its components and reports the percentage that is the target peptide. A higher percentage — commonly ≥98% for quality research material — means fewer impurities. It's the "how pure" number.

How do I know a COA is legitimate and not reused?

Match the lot number on the COA to the number printed on your vial — that's the key check. A real COA is batch-specific and usually includes a chromatogram; a generic PDF with no lot number, no graph, and the same round number across every product should be treated as unverified.

Does a higher milligram vial mean higher purity?

No. Milligrams are mass (how much peptide is in the vial); purity is the percentage that's the target compound, measured by HPLC. They're independent — a 99% pure vial is cleaner than an 80% pure vial regardless of the milligram size. Judge purity by the COA.