How to Compare COAs Between Peptide Vendors

By the NorthPeptide Research Team  |  February 7, 2026

Why COA Comparison Matters

The research peptide market has a trust problem. Because these compounds are not regulated pharmaceuticals, there is no mandatory quality standard. This creates a wide spectrum: from vendors with rigorous third-party testing and batch-specific documentation to vendors who photoshop COAs or use one document across multiple products. Knowing how to read and compare COAs is the most important skill for a research purchaser.

The Four Components of a High-Quality COA

1. HPLC Purity Data

High-Performance Liquid Chromatography (HPLC) separates the components in a sample and shows what percentage of the total area corresponds to the target compound. A minimum acceptable purity for research-grade peptides is typically 98%+. Look for: the specific purity percentage (not just “>98%”), the chromatogram image, the column type, solvent gradient, and the date of analysis.

2. Mass Spectrometry (MS) Identity Confirmation

As covered in our mass spectrometry guide, MS confirms that the compound in the vial is actually the peptide on the label. A COA without MS is incomplete — it tells you purity but not identity. Look for: observed molecular weight, theoretical molecular weight, instrument type, ionisation mode, and charge state data.

3. Third-Party Testing Laboratory

The most trustworthy COAs come from independent laboratories that have no commercial relationship with the vendor. The lab name should be verifiable — it should exist on the internet, have a website, and ideally be ISO 17025 accredited (the international standard for testing laboratories). If the vendor says “tested in-house” without third-party verification, that is a yellow flag. If no lab name is provided at all, that is a red flag.

4. Batch-Specific Identification

Every COA should include a batch or lot number that matches the product you are purchasing. The batch number should appear on both the COA and the product label/vial. Generic COAs with no batch number — or where the same COA is used for all orders regardless of batch — mean the document may not represent your specific product.

Side-by-Side Comparison Framework

When comparing two vendors selling the same peptide, use this framework:

Common Tactics Used by Low-Quality Vendors

• Screenshot COAs: Low resolution images that cannot be zoomed or verified — often indicate the document has been altered
• Shared lab reports: The same PDF used across different products or multiple vendors (you can sometimes find these with a reverse PDF search)
• Missing purity value: Chromatogram shown but the actual purity percentage is absent — the image may look legitimate but carries no verifiable number
• Incorrect theoretical MW: When the COA’s listed theoretical MW doesn’t match known databases for the peptide — suggests copy-paste errors from a different compound’s COA
• Lab doesn’t exist: The lab named on the COA cannot be found online or does not have an accreditation listing

How to Verify a Lab

Search the lab name on Google. A legitimate testing laboratory will have a website, a physical address, and often an accreditation listing in the A2LA (American Association for Laboratory Accreditation) database or equivalent national body. You can also contact the lab directly and ask if they tested a specific batch — a real lab with real records can confirm this.

References