A plain-English guide to the one document that actually tells you what is in a research peptide vial, and how to read it in under a minute.
A certificate of analysis, or COA, is a laboratory report describing what is actually inside a product. For a research peptide it usually answers two questions: is this the compound the label claims, and how pure is it. Think of it as the difference between a restaurant telling you a dish is fresh and an inspector handing you the lab result. The COA is the evidence behind the claim.
A useful COA names the compound, gives the measured purity as a percentage, states the analytical method used, identifies the laboratory, and usually carries a batch or sample reference and a date. Many also include a chromatogram, the graph the testing instrument produces. If a document is missing the method, the lab name, or the actual purity figure, it is closer to a marketing image than a real certificate.
The standard tool is high-performance liquid chromatography, or HPLC, which separates the contents of a sample so each component can be measured. The main peak represents the target peptide, and its size relative to everything else gives the purity percentage. Identity is typically confirmed by mass spectrometry, which weighs the molecule to check it really is the peptide claimed. Together these answer "what is it" and "how much of it is the real thing".
A COA from an independent third-party lab is far more trustworthy than one a seller produces in-house, for the obvious reason that an outside lab has no stake in the result. Janoshik is a commonly used independent lab in this space. When a COA names a recognised external laboratory and you can cross-check the report, the claim stops being marketing and becomes evidence.
Open the report and check four things in order: the compound name matches what you are buying, the purity figure is present and high (commonly above 98 to 99 percent for quality material), a named independent lab issued it, and the date and batch are recent and specific. If all four hold up, the document is doing its job. If any are vague or missing, treat the purity as unconfirmed.
A COA is powerful but not magic. It reflects the sample that was tested, not necessarily every vial ever sold under that name, which is why recent, batch-specific testing matters more than a single old certificate. It also says nothing about storage after testing, sterility, or how the product should be handled. Use it as the strongest single signal of quality, not the only one.
Research-use information only. Not medical advice.