Reading a COA: what 2%, assay-verified means

There are two kinds of percentage in skincare, and they are printed identically.

The first is a formulation percentage. Someone weighed an ingredient into a batch and did the arithmetic. It is a statement about intent.

The second is an assay. Someone took finished product off the line, ran it through an analytical method, and measured what was actually in it. It is a statement about fact.

Almost every number you have read on a skincare carton is the first kind.

Why the two diverge

Even with honest intent, the measured figure drifts from the formulated one. Raw materials vary in purity. Active can be lost during manufacture — to heat, to pH, to time in a mixing vessel. Complexes can partially dissociate. A peptide weighed in at 2% can assay lower by the time it is in a bottle.

Independent testing of copper peptide products has repeatedly found finished goods measuring well under their label claims. The active works. The label is frequently optimistic.

What a certificate of analysis is

A COA is the document that accompanies a manufactured batch. At minimum it should carry a batch identifier, the date, the method used, what was tested for, and the result.

Three details separate a meaningful COA from a decorative one.

What was tested. A certificate for the raw material tells you about a drum of powder a supplier sold. A certificate for finished product tells you about the bottle in your hand. These are not the same document and the difference is the entire point.

Which method. For peptides, high-performance liquid chromatography — HPLC — is the standard. It separates the components of a mixture and quantifies them individually.

Which batch. A COA describes one batch. A brand publishing a single certificate from 2023 and applying it to everything since is showing you a document, not a practice.

How to read ours

The current batch of the Aijaé Peptide Serum is AJ-0426. It was assayed by HPLC in finished product and measured 2.03% copper tripeptide-1.

Three things about that number are deliberate.

It is finished product, not raw material. It is measured, not calculated. And it is 2.03%, not 2% — because 2.03% is what the instrument returned, and rounding to a marketing-friendly figure would quietly convert a measurement back into a claim.

The batch number is printed on your bottle. The certificate is available on request, and the request is not a test you have to pass.

What to ask any brand

Four questions, in order of how much they reveal.

Is your stated percentage formulated or assayed? Was it measured in finished product or raw material? Which method? Can I see the certificate for the batch I received?

Most brands cannot answer the second question, and the inability is the answer. A brand that measures knows immediately; a brand that calculates has to go and ask someone.

Why we do it this way

None of this is difficult or expensive. Batch assay is routine analytical work, and the reason it is unusual in cosmetics is not cost — it is that nobody is required to, and an unmeasured number can be whatever the marketing needs it to be.

We publish the measured figure because a serum priced like ours should be able to prove what is in it. If the number ever comes back low, we would rather print the low number than quietly ship it.