A Certificate of Analysis (COA) is the single most useful document a research-compound supplier can give you — but only if you know how to read it. A COA is not a marketing sheet; it is a lab-generated record of what a specific batch actually contains. This walkthrough goes field by field so a researcher can evaluate one with confidence, strictly within a research-use-only (RUO) framework.
A framing note: everything below concerns laboratory research materials and their testing documentation. Nothing here is guidance for human use, and no therapeutic, disease, cure, or treatment claims are made or implied.
Header fields: who, what, and which batch
The top of a COA should establish traceability before any test result:
- Product name and CAS/identifier — the compound the document describes. Confirm it matches what you ordered.
- Lot / batch number — the most important field on the page. A COA is only meaningful if its lot number matches the label on the vial in your hand. A generic "typical values" sheet with no lot number is a specification, not a certificate.
- Date of analysis / manufacture — tells you how current the testing is.
- Issuing laboratory — the lab that ran the analysis. Note whether it is the supplier's in-house lab or an independent third party.
If the header cannot tie the document to a specific physical batch, the rest of the numbers cannot be trusted to describe what you received.
Identity: is it actually the right compound?
- Mass spectrometry (MS) — confirms molecular identity by measuring molecular weight. The reported mass should match the theoretical mass of the target compound. This answers "is this the right molecule?"
- Molecular formula / theoretical mass — the reference value the MS result is checked against.
Identity testing is distinct from purity. A sample can be the correct compound (good identity) but still contain impurities (lower purity), so both matter.
Purity: how much of it is the target compound?
- HPLC purity (%) — High-Performance Liquid Chromatography separates the sample into its components and quantifies the target as a percentage of the total. This is the headline "99.x% pure" figure — but it only means something with a method and a lot-matched result behind it.
- Chromatogram — the visual trace from the HPLC run. A clean single dominant peak is what you want; multiple significant peaks indicate impurities.
- Impurity profile — some COAs characterize what the non-target fraction is. More detail is better.
Be skeptical of a purity percentage printed with no chromatogram and no method — the number alone is unverifiable.
Contamination screening
- Heavy-metal screening — tests for elements such as lead, arsenic, cadmium, and mercury. This is a core quality question that many suppliers still omit. Look for actual results, not just an assurance that testing "is done."
- Endotoxin / bioburden (where applicable) — additional contamination measures some labs report.
Methods and specifications
- Test methods — the COA should name the analytical methods used (e.g., HPLC for purity, MS for identity). Named methods make the results auditable; vague "high purity" claims do not.
- Specification vs. result — good COAs show the acceptance specification (e.g., "≥98%") alongside the measured result (e.g., "99.2%"), so you can see the sample passed against a defined standard.
Signatures and traceability
- Analyst / approver signature — indicates a person stands behind the result.
- Third-party lab identification — independent testing carries more weight than in-house QC because there is no conflict of interest.
- Lot linkage throughout — the lot number should appear consistently so the document, the tests, and the vial are provably the same batch.
Putting it together: a quick checklist
When you pick up a COA, confirm you can answer yes to each:
- Does the lot number match my vial?
- Is identity confirmed by mass spectrometry?
- Is purity quantified by HPLC, with a chromatogram?
- Are heavy-metal results present?
- Are the methods named?
- Was any of this done by an independent third party?
- Is the whole document traceable to one batch?
If a supplier cannot produce a document that answers these, the claim is unverified — regardless of how the marketing reads. You can see worked examples of lot-specific COAs on our COAs & Testing page, and a plain-language definition of every term above in our glossary of research-peptide and lab-testing terms.
This article is provided for informational purposes only and describes laboratory research materials and their testing documentation, intended strictly for research use only (RUO). The compounds and documents referenced are not for human or veterinary use, and nothing herein constitutes medical, therapeutic, or diagnostic advice, nor any claim to treat, cure, prevent, or diagnose any condition. All research materials must be handled by qualified professionals in appropriate research settings in accordance with applicable laws and regulations.