How to read a certificate of analysis without guessing

Key takeaways

A COA describes one submitted sample. Not a whole vendor, not a batch, not your future order.
Identity, purity, and quantity are three separate results. A strong one does not cover a missing one.
In our ledger, a 99.4%-pure GHK-Cu sample was 22.7% short on dose. Purity did not catch it.
Trust records hosted by the lab over screenshots, and keep your conclusion the size of the sample.

Start with what was tested, not with the numbers

Someone sends you a certificate of analysis, and your eye goes straight to the big purity percentage near the top.

Start somewhere else.

Look first for a sample label, a batch or lot number, a test date, a lab record number, and a link back to the record on the laboratory's own site.

When those fields are missing, you often can't connect the document to the thing being sold at all. You're looking at a PDF about a vial, with no way to know if it's the vial in the listing.

A vendor or manufacturer name on a lab listing is attribution that arrived with the sample. Somebody submitted material and told the lab whose it was.

That's worth knowing, and it isn't proof that the named party made the material. It also isn't proof that everything sold under that name is the same thing.

Identity, purity, and quantity are three different questions

They get collapsed into "it's tested" constantly, so it's worth separating them.

Test	The question it answers	What it can't tell you
Identity	Is the compound the one on the label?	How much of it there is
Purity	What share of the material is the target?	Whether the dose is right, or whether it's sterile
Quantity	Does the measured mass match the claim?	Whether the material is what it says

A strong result in one column does not fill a gap in another.

We keep an open testing ledger of 117 certificates, covering 11 compounds and 38 named parties, each linked to its original lab record.² Two entries in it show exactly how far apart purity and quantity can drift.

Both are GHK-Cu. Both are labelled 100mg. Both came back above 99% pure.

GHK-Cu sample	Purity	Claimed	Measured	Off by
Sample A	99.435%	100mg	77.27mg	−22.7%
Sample B	99.598%	100mg	124.36mg	+24.4%

One vial held nearly a quarter less than the label promised. The other held nearly a quarter more.

Read only the purity column and both look excellent. Purity was never going to catch this, because it isn't the question purity asks.

And neither number says anything at all about sterility, endotoxin, microbial contamination, or leftover solvents.¹ Those tests mostly aren't run, and a test that wasn't run is not a pass.

This matters more for peptides than for most compounds, because they're almost always injected rather than swallowed.³ Contamination that a digestive system would handle goes straight into tissue instead.

Read the scope before you read the result

Three things decide how much a document is worth.

Which methods were used. A purity figure is a figure produced by a specific method. Different methods can give different answers on the same vial.

What went unreported. Look for the tests that aren't there. A report showing identity and purity, with nothing on sterility, is a narrow document being presented as a broad one.

Whether you can verify it. A record hosted by the laboratory itself is stronger provenance than a screenshot or a repost.¹ Screenshots can be edited, and they usually can't be traced back to anything.

In our ledger, every one of the 117 records carries a link to the original lab document, because a result you can't check is a claim rather than evidence.

Keep the conclusion the size of the sample

This is the rule that does the most work, and it's the one most often broken.

The result describes the vial that was submitted, on the date it was submitted.

Stretching it to another vial, a later lot, or the vendor's current inventory needs more evidence than one document can carry. Most COAs in circulation are being asked to prove far more than they can.

A reasonable read sounds like this: this sample, on this date, tested at this purity and this mass, by this method, and here's the lab record.

An unreasonable one sounds like this: they're tested.

For the wider checklist that a COA fits inside, see how to evaluate a peptide vendor. For the basics of what these compounds are, start with what peptides actually are.

Frequently asked questions

Does a certificate of analysis prove a product is safe?

No. A COA reports the tests that were run on one submitted sample. Most peptide COAs report identity and purity only, which means they say nothing about sterility, endotoxin, or residual solvents. A test that was not run is not a pass.

What does the purity percentage actually measure?

It estimates what proportion of the measured material is the target compound, under whatever analytical method the lab used. It does not tell you whether the vial contains the amount of that compound the label claims, and those two things come apart more often than people expect.

Can one COA cover a vendor's whole product line?

No. The result describes the vial that was submitted. Applying it to a different vial, a later lot, or an entire catalogue requires more evidence than one document can provide.