A Certificate of Analysis (COA) is the single most important document attached to a research peptide order. It is the independent, third-party record confirming what is actually in the vial — not just what the label claims. Yet most buyers skim past it without understanding what each section means, or how to tell a rigorous COA from a cosmetic one. This guide walks through a real COA section by section.
What a COA Is — and Isn't
A COA is a report issued by an analytical laboratory after testing a specific batch (lot) of material. It is not a safety certification, a regulatory approval, or a guarantee of biological activity. It answers two narrow, testable questions: (1) is the molecule what it claims to be (identity), and (2) how pure is it (purity)? Everything else — intended use, handling, storage — is outside its scope.
A legitimate COA is always tied to a specific batch or lot number, because purity and identity can vary between production runs. A document that never references a batch number, or that is reused across every product on a site regardless of batch, is not functioning as a real COA — it is a template.
Identity Testing: Confirming the Molecule
Identity is most commonly confirmed with mass spectrometry (MS), which measures the mass-to-charge ratio of the molecule and its fragments. A COA should report an observed molecular weight that matches the expected molecular weight of the peptide within a small tolerance (typically under 0.1–0.5%). Some labs also report amino acid sequencing or a fragmentation pattern as further confirmation. If a COA lists only a purity percentage with no mass spec or identity data at all, that is a meaningful gap — purity alone cannot tell you the vial contains the right molecule, only that whatever is in it is relatively uncontaminated.
Purity Testing: HPLC
Purity is typically reported via High-Performance Liquid Chromatography (HPLC). In an HPLC purity test, the sample is passed through a column that separates components by their chemical properties; a detector then records each component as a peak on a chromatogram. The area under the main peak, expressed as a percentage of the total peak area, is reported as the purity figure — most reputable research peptide suppliers report ≥98–99% purity by HPLC.
A few things are worth checking on the chromatogram itself, not just the summary number: a single sharp, symmetric main peak is a good sign; multiple smaller peaks (impurities or truncated/failed synthesis sequences) should be disclosed, not cropped out of the image. If a COA shows only a number with no chromatogram image, ask the supplier for the underlying trace.
Reading the Batch Number
Every COA should reference a specific batch or lot number, and that same number should appear on the product label or vial. This is what lets a batch-specific COA actually mean something — it ties the document to the physical material you received, rather than to the product line in general. If the number on your vial doesn't match the number on the COA you were given, the documents are not for the same material.
Who Performed the Testing
A rigorous COA names the testing laboratory, and ideally that lab is independent of the manufacturer or seller — third-party testing removes the incentive to under-report impurities. Some labs are accredited to ISO/IEC 17025, the general standard for testing and calibration laboratory competence; while not every peptide-testing lab carries this accreditation, its presence is a positive signal.
Red Flags in a COA
- No batch number, or a batch number that doesn't match the product.
- No identity confirmation (mass spec) — purity percentage only.
- A chromatogram image that looks reused, mismatched in formatting, or inconsistent with the stated date.
- No named testing laboratory, or a lab that cannot be independently verified.
- A document date far removed from any plausible production or testing timeline.
What This Means for Your Research
A COA doesn't make a claim about what a compound does — it documents what a specific batch of material is and how pure it is, nothing more. Treating it that way, and actually reading the identity and purity sections rather than just the final percentage, is the difference between a document that informs your research records and one that's just decoration on a product page.
Sources
- U.S. Pharmacopeia (USP) General Chapter <621> Chromatography — HPLC methodology standards
- International Council for Harmonisation (ICH) Q2(R2) — Validation of Analytical Procedures
- ISO/IEC 17025:2017 — General requirements for the competence of testing and calibration laboratories
- FDA Guidance for Industry: Analytical Procedures and Methods Validation for Drugs and Biologics
For research use only. Not for human or veterinary consumption.