A certificate of analysis, usually shortened to COA, is the document a testing laboratory issues after it examines a sample. For anyone who works with research peptides, it is the only record that connects a product on a shelf to measured data. Reading one well takes a few minutes once you know where to look.
Start with the header
The top of a report identifies who did the work and what was tested. Look for the laboratory name, a task or report number, the dates the sample was received and the analysis was conducted, and the sample name. Some laboratories also print a verification key or QR code so a reader can confirm the report on the laboratory’s own website. If the header is missing or the sample name is vague, read the rest of the page with caution.
Match the batch number
The batch number (sometimes called a lot number) is the link between the report and the vial in your hands. The number printed on the report should match the number on the product record. A certificate for a different batch tells you about that batch only. Our batch numbers guide explains this in more detail.
Find the method
The method line states how the result was produced. For peptides this is most often reversed-phase HPLC with UV detection, written as RP-HPLC or HPLC-UV. Some reports add LC-MS, which measures molecular mass and so speaks to identity rather than purity. Our comparison of HPLC and LC-MS covers the difference.
Understand the purity figure
A purity percentage on an HPLC report describes the share of the total detected signal that belongs to the main peak. It is a relative measure under one set of conditions. It does not say anything about substances that the detector cannot see, and a high figure on its own does not confirm that the main peak is the compound named on the label. That is why identity data, where it is available, is worth reading next to purity.
Check the quantity line
Some reports list a measured amount of the compound in the vial as well as purity. Measured amounts normally fall within a range around the labelled strength, because weighing, vial filling and measurement each carry a small tolerance. Two replicate readings, where printed, give a feel for that spread.
Look for endotoxin
Endotoxin results, reported in endotoxin units (EU) per vial, come from a separate assay and are printed on some reports and not others. They matter for cell-based work, where endotoxin can interfere with results. Our endotoxin testing explainer describes what the number means.
Read the fine print
Comments, the sample description and the tests-requested line are easy to skip, yet they tell you what the laboratory was actually asked to do. A test requested as a general screen is different from a test designed for one specific compound.
A worked example
Our Tirzepatide 15 certificate lists the laboratory (Janoshik), the analysis date, the batch number, HPLC-UV as the method and a purity figure, with endotoxin reported separately on our library listing. Follow the same order each time: laboratory, batch, method, purity, quantity, endotoxin, comments.
Common questions
Is a certificate the same as a guarantee? No. It is a record of what one laboratory measured in one sample on one date, using one method.
Can two certificates for the same product differ? Yes. Different batches, laboratories and methods produce different numbers, and small differences between replicate readings are normal.
What if something is unclear? Contact us with the batch number and we will point you to the report.
Where to find ours
Every certificate we have published is collected in the COA library, searchable by product. Not every listing has a published certificate yet, and each product page says whether one is available. For background on how we approach testing, see Lab Testing & Quality.
All products are sold for laboratory research use only.
