What is a peptide certificate of analysis (COA)?

A peptide certificate of analysis, or COA, is a laboratory report on one specific batch of product. It states whether the material matches the peptide it claims to be (identity), how pure it is (purity), and often whether it is contaminated. A COA describes a tested batch, not a whole product line, so it must be matched to your vial's lot number.

How do you read the purity number on a peptide COA?

Purity on a peptide COA comes from HPLC and is reported as a percentage — the share of the sample that is the intended peptide rather than fragments or byproducts. A figure in the high nineties is common, but a percentage is only as trustworthy as the method behind it, so look for a real chromatogram and a batch-matched result.

Does a peptide COA mean a product is safe or approved for human use?

No. A COA is a quality document, not a use authorization. It reports what an analytical lab measured in a batch; it does not mean the product has been reviewed for human safety, and research peptides are not FDA-approved and are sold for laboratory research use only. A clean COA and safe human use are separate questions.

What is endotoxin testing on a peptide COA?

Endotoxin testing checks for bacterial endotoxin, a membrane component of gram-negative bacteria and a recognised contamination concern in products meant for injection. The standard pharmaceutical method is the LAL test, and results are reported in endotoxin units, abbreviated EU. An endotoxin line shows the vendor is addressing a real safety question that a purity percentage alone does not.

What is the difference between identity and purity on a COA?

Identity and purity answer different questions. Identity, confirmed by mass spectrometry, asks whether the material is the peptide it claims to be — the right molecule. Purity, measured by HPLC, asks how much of the sample is that peptide rather than fragments or contaminants. A batch can be highly pure yet still be the wrong compound, so a strong COA reports both.

How to Read a Peptide Certificate of Analysis (COA)

By MrPepTalks Editorial · Updated 2026-07-16

Learning how to read a peptide certificate of analysis is one of the most useful skills a research buyer can develop, because it is the one document that describes what is actually inside the vial rather than what a label promises. A certificate of analysis, almost always shortened to COA, is a laboratory report on a specific batch of product. It is also one of the most misread documents in the category: buyers often treat a clean COA as proof that a product is safe or fit for human use, when it is neither. This guide walks through a peptide COA field by field — identity, purity, endotoxin, and the batch number that ties the paperwork to your vial — so a marketing page has a much harder time impressing you with a sheet you cannot actually read. It is educational context, not medical advice, and it never tells you to use anything.

What a peptide certificate of analysis actually is

A peptide certificate of analysis is a laboratory document that reports what testing found in one specific batch of product, tied to a batch or lot number. It answers two core questions — is the material the compound it claims to be (identity), and how pure is it (purity) — and often a third, whether it is contaminated. Read it as evidence about a batch, not a general statement about a product line. A COA generated on last year's batch says nothing reliable about the vial shipped to you today, which is why the batch number matters as much as the numbers beside it. A vendor that publishes real, batch-matched certificates is inviting outside scrutiny; one that cannot produce a COA for the exact batch it is shipping is asking you to take identity and purity on faith.

Purity: what the HPLC percentage means

Purity is the number most buyers look at first, and on a peptide COA it almost always comes from high-performance liquid chromatography, abbreviated HPLC. The method separates the sample into its components and reports purity as a percentage — the share of the material that is the intended peptide rather than truncated fragments, byproducts, or other related impurities. A figure such as 98% or 99% means the assay found that proportion of target peptide in the tested sample. Two cautions keep the number honest. First, a percentage is only as trustworthy as the method and the trace behind it: a credible sheet shows the actual chromatogram, not just a hand-typed value, and HPLC is the established workhorse for this measurement. Second, purity is not identity — a sample can be highly pure and still be the wrong molecule, which is exactly why the next field matters.

Identity: what mass spectrometry confirms

Identity is confirmed by mass spectrometry, usually shown on a COA as MS. Every peptide has an expected molecular mass determined by its sequence; the instrument measures the mass of the material in the vial and checks it against that expected value. A match is strong evidence that the batch really is the peptide named on the label. More thorough sheets go a step further with tandem mass spectrometry, or MS/MS, which reads the sequence itself and can characterise the impurities a purity percentage only counts. This is why the strongest certificates pair an HPLC purity figure with an MS identity confirmation: purity tells you how much of the sample is a single peptide, and identity tells you whether that peptide is the right one. A sheet that reports one without the other, or uses vague wording in place of a real instrument readout, is telling you less than it appears to.

Endotoxin and contamination: the safety-adjacent fields

Beyond identity and purity, a thorough COA reports contamination testing, and for material that could end up in solution the most important line is endotoxin. Bacterial endotoxin is a component of the outer membrane of gram-negative bacteria, and it is a recognised contamination hazard in parenteral-grade products; the standard pharmaceutical screen for it is the LAL test, which detects and quantifies endotoxin in units abbreviated EU. A COA that reports an endotoxin result is engaging with a real safety question that a purity percentage alone does not touch. Heavy-metal and elemental-impurity testing belongs in the same category. This is not abstract: when researchers profiled falsified peptide products bought from illegal online pharmacies, they found purity ranging widely from roughly 5% to 75% and toxic elemental impurities including arsenic and lead. The lesson is not that every unlabelled vial is dangerous — it is that without a real, batch-matched COA covering purity, identity, and contamination, you have no way to know.

The batch match: tying the paper to your vial

A certificate of analysis is only meaningful when it is tied to the exact batch you receive. Every real COA carries a batch or lot number and a test date, and that number should match the one printed on your vial. A sheet with no batch number is a generic template, not proof about your product; a sheet for a different lot is proof about someone else's. This is the quiet failure point buyers miss most often. A vendor can publish one genuinely excellent COA as a showcase and then ship unrelated batches against it for a year. So the check is not merely whether a COA exists, but whether there is a COA for this lot, dated recently, with a batch number you can match. The paperwork and the product have to point at each other.

Who ran the test: in-house versus third-party

A COA is only as independent as the lab that produced it. A certificate generated by the vendor's own laboratory is better than nothing, but the seller has an obvious stake in the result. A COA from an independent, third-party laboratory — one with no financial interest in the sale — is the stronger signal, because the tester and the seller are different parties. When you weigh a sheet, look for whether the testing lab is named, whether the result is matched to the batch being sold rather than a one-off showcase, and whether contamination testing appears alongside identity and purity. Reading the COA is one half of sourcing diligence; the other half is judging the vendor around it, which our companion guide at /learn/how-to-vet-a-peptide-vendor covers in full, from red flags to the reputation signals a certificate cannot show.

Why a COA is a quality document, not a use authorization

Here is the distinction that anchors everything above: a certificate of analysis is a quality document, not a use authorization. It reports what an analytical lab measured in a batch. It does not mean the product has been reviewed for safety in people, and it is not FDA-approved for human use. Almost every research peptide sold online is labelled for laboratory research use only, not for human consumption, precisely because it has not gone through that regulatory review. A spotless COA and that research-use-only status are two separate facts that sit side by side: the paper can confirm a batch is pure and correctly identified while the product remains something no regulator has reviewed for human use. Reading the COA well protects you from one specific failure — a mislabelled, impure, or contaminated batch, the kind the falsified-product research above documented. It cannot tell you whether using the compound is wise, safe, or legal, and it was never designed to. For that fuller picture, our guides at /learn/are-peptides-safe and /learn/how-to-read-a-peptide-study weigh the reported risks and the evidence in the same neutral spirit.

Putting it together: a COA reading checklist

You do not need to be an analytical chemist to read a peptide certificate of analysis. Run six checks on any sheet a vendor shows you. One: is there a batch or lot number, and does it match your vial? Two: is there a recent test date? Three: does an HPLC purity percentage appear, ideally with a chromatogram rather than a bare number? Four: is identity confirmed by mass spectrometry? Five: is there contamination testing, such as an endotoxin or heavy-metal result? Six: who ran the test — the vendor, or an independent third-party lab? A sheet that passes all six is doing real work; one that dodges them has told you what it is. And remember the boundary that no certificate crosses: a COA can describe the quality of a batch, but it is not permission to use the compound, which stays for research use only and not FDA-approved for human consumption. Pair this reading skill with honest vendor vetting and an honest look at the evidence, and a confident sales page loses most of its power over you.