A certificate of analysis is a lab’s report on a sample it received. It tells you what a third party measured, on one sample, on one date. That is genuinely useful, and it is narrower than most people assume.
Here is how to read one properly, field by field.
Batch or lot identifier: read this first
This field determines whether the document means anything to you, and it is the one most often filled in badly.
A COA is only evidence about the material it was drawn from. If the batch field says something like “Silver/grey” (a cap colour), the report cannot be tied to a specific production lot. It tells you that a sample of a batch tested well. It cannot tell you that the vial in your hand came from that batch.
A useful batch field looks like a lot number: an alphanumeric code that also appears on the vial or packaging. If those two do not match, the COA is a reference document, not a certificate for your unit.
Client
The company that ordered and paid for the test. This is not always the company selling the product. A distributor may be showing a manufacturer’s COA, or a report from a group buy.
Neither is inherently a problem, and supplier-level testing is normal. But it is worth knowing which you are looking at, because “we test our product” and “our supplier tested a batch” are different statements.
Dates
Three matter: ordered, received, and analysis conducted. Peptides degrade, so a report from eighteen months ago describes material as it was eighteen months ago. Recent is better.
Purity
The headline number, usually from HPLC (high-performance liquid chromatography). The instrument separates a sample’s components by how they move through a column, and purity is the target peak’s area as a percentage of total peak area.
A result of 99.9% means that of everything the detector saw, 99.9% of the signal was the target compound.
Two things about that sentence carry weight. First, “of everything the detector saw” makes this a relative measure. It does not count anything the method cannot detect, and many salts, residual solvents and water fall outside it. Second, duplicate values are a good sign: a report showing two close results ran the analysis twice, which means the measurement is reproducible. A single number tells you less.
Quantity
Often reported as mass. This is a content or fill test: how much of the compound was actually in the vial, versus the labelled amount. It is a separate question from purity. A vial can be extremely pure and underfilled, or correctly filled with impure material. Both numbers matter, and they answer different questions.
Identity
The strongest reports include a mass spectrometry result confirming the compound’s molecular weight matches what it should be. HPLC purity tells you a sample is mostly one thing. Mass spectrometry tells you that thing is the right thing. A COA with purity but no identity confirmation leaves the more basic question open.
Verification key
Reputable labs print a task number and a unique key so anyone can confirm a report is authentic on the lab’s own site. Janoshik, the most commonly used lab in this category, does this.
Always verify. Certificates are easy to alter in a PDF editor, and altered ones circulate widely. A report without a verification mechanism is a claim, not a certificate.
What a purity COA does not tell you
Sterility. HPLC says nothing about microbial contamination. A sample can be highly pure and non-sterile.
Endotoxin. Bacterial endotoxins are fragments of gram-negative bacterial cell walls. They survive standard sterilisation, and a purity assay does not detect them. Endotoxin testing is a separate, inexpensive test that most sellers simply do not order.
Batch uniformity. One sample from one batch is one sample. It does not establish that every unit in the batch is equivalent.
Stability over time. A COA is a snapshot at the analysis date. It does not describe what the material looks like after shipping and storage.
Anything about use. A COA is an analytical document. It states what a compound is and how pure it is. It makes no statement about what the compound does.
A checklist
- Does the batch identifier match the product you have?
- Who is the client: seller, manufacturer, or a third party?
- How recent is the analysis date?
- Is purity reported in duplicate, with close agreement?
- Is there a quantity result alongside purity?
- Is identity confirmed by mass spectrometry?
- Is there a verification key, and did you use it?
- What is not on the report? Sterility, endotoxin and stability are usually absent unless ordered.
A COA that survives all eight is a strong document. Most do not, and knowing which questions a given report leaves open is more useful than a percentage on its own.
NXT Labs products are sold strictly as research chemicals for in vitro research, laboratory testing and analytical purposes only, and are not intended for use in any human or animal application.
