May 30, 2026

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

If you're sourcing research peptides, you've seen vendors claim "99% purity." But how do you verify that? The answer is the Certificate of Analysis (COA) — and knowing how to read one separates serious researchers from everyone else.

What Is a COA?

A Certificate of Analysis is a document from an independent laboratory that verifies a compound's identity and purity. For research peptides, a legitimate COA typically includes two analytical methods:

• HPLC (High-Performance Liquid Chromatography) — measures purity as a percentage
• Mass Spectrometry (MS) — confirms the molecular weight matches the expected compound

How to Spot a Fake COA

Unfortunately, some vendors fabricate COAs. Here's what to check:

1. Third-party lab, not in-house. The COA should come from an independent testing facility, not the vendor's own equipment.
2. Batch/lot number matches your order. A real COA is tied to a specific production batch.
3. Date is recent. Purity degrades over time. A COA from 2022 is meaningless for a 2026 shipment.
4. Full chromatogram, not just a number. A legitimate COA shows the HPLC trace — peaks, baseline, integration. A standalone "99.2%" is worthless.
5. Contactable lab. The testing laboratory should be named and verifiable.

Understanding HPLC Purity Numbers

HPLC purity is reported as a percentage of the main peak area relative to total peak area. But there's nuance:

• 98%+ is standard for research-grade peptides
• 99%+ is excellent and indicates careful synthesis and purification
• Below 95% — the impurities may interfere with your research
• ">99%" with no decimal is suspicious — real HPLC reports decimals

Mass Spectrometry: Confirming Identity

Purity tells you how clean the sample is. Mass spectrometry tells you if it's actually the compound you ordered. The MS report shows the molecular ion peak — it should match the expected molecular weight of your peptide within 0.5 Da for low-resolution MS, or within 5 ppm for high-resolution.

The Bottom Line

A vendor who won't share COAs publicly, or whose COAs lack full chromatograms and third-party lab attribution, is not one you should trust with your research. At Polypeptides, every product listing includes its batch-specific COA — because transparency is the only standard that matters.

→ Browse all products with verified COAs