Peptide certificate of analysis (COA): What it is and how to read it

A peptide certificate of analysis (COA) shows what a laboratory found when it tested a particular peptide sample. Depending on the tests performed, the report might include the peptide's identity, measured amount, chromatographic purity, related impurities and other results. But the numbers aren't always as straightforward as they look. A report showing 99.82% purity and 100.0% assay, for example, isn't necessarily contradicting itself. Those figures may describe two different measurements. So what should you actually look for in a peptide COA, and how do you make sense of the results? What is a peptide certificate of analysis (COA)? A Certificate of Analysis is a record of laboratory testing. It identifies the material examined and shows the results of the analyses performed. For a peptide sample, the certificate brings those findings together in one document. For research peptides, a COA may come from the manufacturer or from an independent laboratory. The difference is worth understanding. A manufacturer's certificate usually forms part of its quality-control documentation. An independent laboratory, meanwhile, reports on a sample it received for testing. That laboratory may have no direct involvement in manufacturing the material. Neither type of document tells the whole story on its own. What matters is the information it contains, which tests were carried out and how the tested sample relates to the material being evaluated. It's also useful to distinguish a COA from a product specification. A specification sets out what a material is expected to meet. A COA shows the results obtained during testing. If a specification requires a certain result, the certificate may show whether the tested sample met that requirement. Think of it as the difference between a target and a measurement. One tells you what is expected; the other tells you what was found. That's the practical peptide COA meaning: a certificate provides analytical evidence about a sample, rather than simply describing the product as high quality. What information does a peptide COA contain? Open two certificates from different laboratories and they may look completely different. One might be a single page with a few results. Another could include several pages of data, chromatograms and technical notes. There is no universal layout that every peptide laboratory follows. Still, most reports contain the same basic types of information. The details may vary depending on the peptide and the scope of the analysis. Sample details tell you what was submitted for analysis. You'll usually see a peptide name, a sample description and some form of identification number. A laboratory might assign a task number or report ID. The manufacturer may also provide a batch or lot number. These numbers are easy to confuse, but they have different jobs: one identifies the laboratory record, while the other is intended to identify a production lot. For a closer look at how test results are connected to individual production batches, see our guide to  batch coa . Laboratory information tells you who carried out the analysis. Depending on the report, you may also find contact details, an issue date or the name of an authorised signatory. Dates show when the sample was received and tested. Some reports include the date testing was ordered as well. These aren't necessarily the same day, particularly when several analyses are involved. Test results are usually the part readers go straight to. They might include percentages, measured quantities, concentrations or short findings such as “Confirmed” and “Pass”. Methods and limits explain how the results were obtained and what they mean. Sometimes this information appears beside each result. In other reports, it's tucked away in a footnote or separate laboratory document. One important detail is often overlooked: a certificate only covers the tests listed on it. If a report contains HPLC and mass spectrometry results but says nothing about endotoxins, there's no basis for assuming endotoxin testing was performed. Reading a real peptide COA: Melanotan II example Let's look at a supplied certificate rather than another list of definitions. The laboratory report identifies the sample as Melanotan II (10 mg). This gives us a concrete example of how a certificate presents its findings. It includes task number  572413, batch number AR1636RT2 and names ShiLai Peptide Technologies as the client and manufacturer. The document records three dates: testing was ordered on 3 June 2026, the sample arrived on 8 June and the analysis took place on 10 September. There's a considerable gap between receiving and analysing the sample. That isn't enough to conclude that something went wrong, but it does raise a reasonable question: how was the material stored during that period? The report dates alone don't answer it. Now look at the results. These figures come from the supplied certificate and are used here to explain how laboratory reports are read. The document and its results have not been independently verified with the issuing laboratory. At first glance, the report looks simple enough. Most results are expressed as a number or a short statement. But there are a few details worth examining. The sample is described as 10 mg, yet the laboratory reports a content of 10.93 mg. Is that a problem? Not necessarily. The first figure may be the nominal quantity, while the second is the amount determined by testing. We'd need to see how the laboratory calculated the result before drawing conclusions. Then there are the two percentages: 99.82% purity and 100.0% assay. It's tempting to compare them directly, but they may be calculated on different bases. And what about “Identity (MS): Confirmed”? That's a positive finding, although the word “Confirmed” doesn't tell us exactly what the laboratory measured or which criteria it used. This is where a COA becomes more interesting than a simple list of numbers. Each result answers a particular question. Understanding those questions is what makes the document useful. Understanding peptide COA test results The analytical section is the heart of a certificate. It's also where misunderstandings tend to happen. People often look for the highest percentage, assume it represents overall quality and move on. Laboratory testing doesn't work quite that way. Different methods examine different properties, and a strong result in one test doesn't replace information from another. Each type of analysis adds something different to the overall picture. HPLC results and related impurities HPLC stands for high-performance liquid chromatography. In simple terms, the technique separates components of a sample so they can be detected and analysed. A laboratory might use HPLC to examine the chromatographic composition of a peptide sample, measure a particular compound or investigate related substances. The distinction matters because not every HPLC percentage represents the same thing. A report may also include a result for related impurities. These are substances covered by the laboratory's impurity-testing method, potentially including compounds associated with synthesis or degradation. That doesn't mean the test searched for every substance that could possibly be present. It tells you about the compounds the method was designed and able to measure. If you'd like to understand the technique itself, our guide to  peptide HPLC analysis  explains what happens during testing and how the results are produced. Peptide identity by mass spectrometry A peptide can produce a convincing chromatographic result and still require separate identity testing. Mass spectrometry (MS) helps answer a different question: are the measured mass-related characteristics consistent with the expected compound? For a peptide, this provides evidence that the tested material matches the expected molecular mass. In the Melanotan II certif