How to Read a Certificate of Analysis

What a certificate of analysis actually is

A certificate of analysis is a report from an analytical laboratory describing one specific batch of one specific material. It states what the laboratory was sent, what tests it ran, what those tests returned, and when.

The three words that matter in that sentence are one specific batch.

A certificate is not a statement about a product line. It is not a statement about a supplier's standards. It describes a defined quantity of material that was synthesised at a particular time, sampled, and measured. The next batch of the same compound is a different batch, and it needs its own certificate, because it is different material.

This is why a supplier publishing a single purity figure across every batch of every product is telling you something. Real measurements vary. Ours run from 99.2% to 99.96% depending on the batch. A number that never moves is not a measurement — it is a claim wearing a measurement's clothes.

Walking through a real one

Open any certificate in our COA Library and you will see roughly the same structure. We will use batch PTX-010, a 50mg vial of 5-Amino-1MQ, as the worked example.

The header

At the top: the laboratory's name and logo, the words Certificate of Analysis, and the client the report was prepared for.

Is the laboratory named, and is it somebody other than the supplier? A supplier testing its own material and issuing its own certificate is not third-party testing. It might be honest. It is not independent, and independence is the entire point of the exercise.

Are there dates? PTX-010 shows a received date of 08/26/2026 and a published date of 09/02/2026 — the lab got the sample, ran it, reported a week later. Dates that are absent, or that postdate the sample being offered for sale, are worth a question.

The sample identification block

This is the part most people skim, and the part that does the verification work. On PTX-010 it reads:

DECLARED IDENTITY    5-Amino-1MQ
MATRIX TYPE          Peptide
SAMPLE NAME          5-Amino-1MQ
SAMPLE SIZE          50.0 mg
LOT CODE             IP-9001

Declared identity is what the client said the material was. Sample name is what the laboratory logged. They should match, and they should match the product you are looking at.

Lot codeis the thread that ties the document to physical material. It should correspond to a batch identifier that exists somewhere you can see it — on the vial label, on the product page, in the supplier's library. A certificate whose lot code appears nowhere else is a document about nothing in particular.

The results

The heart of it. On PTX-010:

Test       Specification   Result                              Status
IDENTITY   5-Amino-1MQ     Conforms 2/2                        Conforms 2/2
QUANTITY   Measure         mean 50.37 mg · SD 0.66             MEASURED
                           %RSD 1.31% · n=2

Read that second row carefully, because it shows you what a real measurement looks like.

The vial is labelled 50mg. The laboratory measured a mean of 50.37 mg across two replicates (n=2), with a standard deviation of 0.66 and a relative standard deviation of 1.31%.

That is not a round number, and that is the point. It measured slightly over label, which is normal and expected. It reports how many times it measured, and how much the measurements varied between replicates. A result reported as exactly “50 mg” with no replicate count and no variance figure has either been rounded into meaninglessness or was never measured at all.

The chromatography

Further down, most certificates include the raw analytical output — typically an HPLC or HPLC-MS/MS trace. It looks like a graph with one large peak and, if the material is clean, very little else.

You do not need to interpret a chromatogram in detail. What matters is that it is present. The purity percentage on the front page is a conclusion. The chromatogram is the evidence that conclusion was drawn from. A certificate reporting a purity figure with no underlying data is asking you to take its word for it.

The four checks

If you do nothing else, do these. They take about ninety seconds.

How reused and fabricated certificates give themselves away

• The same purity figure everywhere. The most common tell. Real assays vary between batches. A catalogue where everything is exactly 99.9% is reporting a marketing target.
• No batch number, or one that appears nowhere else. If the document cannot be tied to physical material, it is not documentation. It is decoration.
• Dates missing, or identical across every product. Batches are tested when they arrive. A catalogue apparently tested on a single day either received everything at once or is publishing one document repeatedly.
• “Available on request.” Certificates that exist are published. Certificates that appear only after a customer pushes are being produced for that customer, which raises the question of what happens for the customers who do not push.
• A purity figure with no chromatogram. A conclusion with the evidence removed.
• Round numbers throughout. Real instruments produce 50.37 mg and 99.65%. They do not produce 50 mg and 99.5% batch after batch.

What the tests actually cover

Certificates report specific tests, and knowing which is which tells you what you are actually being assured of.

• Identity — confirms the material is the compound it is declared to be. This is the baseline. Everything else is meaningless if the identity is wrong.
• Purity — what proportion of the material is the declared compound, usually measured by HPLC. The headline number.
• Net content — how much material is actually in the vial, as against what the label says. This is where underfilling shows up.
• Endotoxin — screens for bacterial endotoxins, which are contaminants rather than a property of the compound itself.
• Microbial sterility screen — a broader contamination check.

Our certificates carry different combinations of these depending on the batch — some cover purity and net content, others add endotoxin screening or a microbial sterility screen. The methods run are stated on each certificate and on each batch's page in our library, so you can see exactly what was and was not tested rather than assuming.

What no certificate covers: a certificate describes the material as it was when the laboratory measured it. It says nothing about how the material was handled afterwards, how it was shipped, or how it has been stored since. That is a separate question and a real one.

Verifying the vial in front of you

The whole point of the preceding pages is this, so it is worth stating plainly.

1. 1.Read the batch number printed on the vial label.
2. 2.Open the supplier’s certificate library and find that batch number.
3. 3.Confirm the compound and strength on the certificate match the vial.
4. 4.Read the purity figure and the date it was tested.

If any step in that chain breaks — the batch number is not in the library, the library does not exist, the certificate is for a different compound — you have documentation that does not describe your material.

We publish every one of our certificates in the COA Library, free and without an account, each with its own page and its own address. You can run the check above on any batch we have sold — including batches you did not buy, and before you buy anything at all.

That is not generosity. It is the only version of this that means anything.