A certificate of analysis (CoA) tells you what’s in a vial; up to a point. It practically never tells the whole story.
A document claiming “99% pure” might look reassuring, but unless you know which batch was tested, which laboratory ran the analysis, which methods were used, and what those numbers actually measure, the percentage alone is not much to go on.
Ultimately, a good CoA turns a vague quality claim into something you can inspect. A weak one is a little more than a nice-looking PDF.
What a Peptide CoA Actually Is
A CoA is a laboratory report tied to a particular sample or production lot. Depending on the product and testing program, it can report identity, purity, quantity, endotoxin levels, water content, and other quality attributes.
Per FDA’s guidance for active ingredients, an authentic certificate must identify the material and batch, outline the tests run, and state the results alongside acceptance limits and numerical results where applicable, as well as identify the manufacturer or relevant testing party. The agency also stresses that the reliability of supplier certificates should be checked periodically rather than accepted blindly.
Identity
Mass spectrometry (MS) is commonly used to provide identity information for peptides. In simple terms, the instrument measures molecular mass and compares the result with what you would expect for the specified peptide.
But identity testing has limits. A matching mass doesn’t automatically prove that every structural detail is correct, nor does it tell you whether the sample contains unwanted material. FDA guidance on analytical methods treats identity, strength, quality, purity, and potency as related but distinct questions.
So if a CoA reports “identity confirmed by MS,” read it as exactly that. It’s useful evidence of identity, but it’s not a claim that the sample is pure, sterile, or therapeutically effective.
Purity
Peptide purity is often measured with HPLC or UPLC. These techniques separate components in a sample and allow the laboratory to assess the proportion attributed to the target material under the stated analytical method.
A reported purity of 99.5%, for example, doesn’t mean “99.5% guaranteed safe.” It means the sample met the laboratory’s stated purity assessment at that level under that method.
This distinction is particularly important to understand with blends. A single percentage for a mixture doesn’t necessarily tell you how much of each individual peptide is present.
FDA research illustrates why peptide purity is more complicated than a single percentage. In one FDA study of five marketed salmon calcitonin products, researchers used HPLC-MS/MS to profile peptide-related impurities and identified more than 120 of them.
Quantity
You also want to separate purity from quantity. A vial labeled with a certain total mass doesn’t necessarily have a CoA that independently establishes the exact amount of every component in that vial. A laboratory may perform a quantitative assay, but the report needs to state what was measured and how.
This is partially why experienced researchers look past the big percentage printed near the top of a certificate. The following details are far more informative:
- What was actually quantified?
- By which method?
- Against what specification?
Endotoxins and Sterility
An endotoxin result, such as a Limulus amebocyte lysate (LAL) test, addresses bacterial endotoxin in the tested sample. It does not prove that a product is sterile.
Sterility is a separate testing question. So are microbial contamination, particulate matter, and other potential quality attributes. FDA materials for injectable products distinguish among sterility, pyrogenicity, endotoxin, and particulate testing for exactly this reason.
The Batch Number Matters Most
Let’s say that a supplier publishes a beautiful CoA from an independent laboratory. Great; now check the lot number. Does the certificate correspond to the exact batch being sold?
Tuned Research, for example, publishes lot-specific third-party reports for its research products and links the relevant documentation to individual products. Its current Klow peptide listing identifies KLOW as an 80 mg lyophilized research blend containing GHK-Cu, BPC-157, TB-500 and KPV, with a report from Horizon Analytical.
There is also a great example of why you should read the actual report rather than assume what it says. The published KLOW report confirms identity by MS and reports an endotoxin result below 0.05 EU/mL, but does not report a numerical combined purity result. Tuned Research therefore does not present a numerical purity guarantee for that blend.
That is actually the sort of transparency you want from a certificate: a company should not turn a blank field into a claim that the laboratory never made.
Red Flags When You Inspect a CoA
A certificate deserves more scrutiny if:
- There is no lot or batch number
- The lot number does not match the product you are buying
- The testing laboratory is unnamed
- The document provides percentages but no testing method
- Results are listed without specifications or acceptance limits
- A “purity” number is presented as proof of sterility, safety, or effectiveness
- A supplier publishes one old certificate and implies it represents every current batch
- The certificate appears to come from the seller but offers no way to verify the laboratory report independently
What a CoA Cannot Prove
A CoA does not establish human efficacy, appropriate dosing, long-term safety, or regulatory approval. For research materials, this distinction is critical: it separates verified laboratory findings from unsupported claims.
Ultimately, a reliable CoA answers five simple questions:
- What was tested?
- Which lot?
- By whom?
- Using what method?
- What did they find?
If you can answer them from the document, you have something genuinely useful. If you only have a giant “99%” printed on a PDF, you have a number. And these are not quite the same thing.