How to Read a Peptide Certificate of Analysis

A certificate of analysis, or COA, is the only document that tells you what is actually inside a vial. Everything else on a product page is a claim. The COA is the evidence.

It is also the document most people glance at, see a percentage above 98, and close. That is a mistake, because a COA can look immaculate and still tell you nothing at all about the vial in your hand.

This guide walks through what each section means, and the five things that quietly make a certificate worthless.

What a certificate of analysis actually is

A COA is a report issued by an analytical laboratory after testing a specific batch of material. It records what the lab was asked to look for, what methods it used, and what it found.

Two things follow from that definition, and both matter more than the purity figure.

First, a COA applies to one batch. Not to a product line, not to a supplier, not to a compound in general. If a supplier synthesises or sources a new batch, the old certificate no longer describes what you are being sent.

Second, a COA only reports what was tested for. A certificate showing 99% purity by HPLC says nothing about bacterial contamination or heavy metals, because HPLC was not looking for either.

The sections, and what they mean

Product name and batch number

The top of the certificate should name the compound and give a batch or lot number. That number is the entire point of the document. It is the thread connecting the paperwork to the physical vial.

Check that the batch number on the certificate matches the batch number printed on the vial you received. If the vial has no batch number at all, the certificate cannot be tied to it, and you are back to trusting a claim.

Test date

A certificate has an age. Testing carried out two years ago describes material synthesised two years ago. For a supplier shipping regularly, a current certificate should be recent relative to the batch.

HPLC purity

High-performance liquid chromatography separates the contents of a sample into its components and measures the relative size of each. The result is usually expressed as a percentage: the proportion of the sample made up by the target peptide, against everything else present.

The trace itself is more informative than the number. A clean chromatogram shows one dominant peak. A trace with several smaller peaks alongside the main one indicates related substances, incomplete synthesis, or degradation, even where the headline figure still reads well.

This is why a certificate that gives a number but no chromatogram is weaker evidence than one that shows the trace.

Mass spectrometry

HPLC tells you how much of the sample is one thing. It does not tell you that the thing is what the label claims. Mass spectrometry does that job, by measuring molecular weight and comparing it against the expected value for the compound.

Purity without identity is only half the picture. A vial can be 99% pure and 99% pure something else entirely. A complete certificate covers both.

Appearance, solubility and water content

These are the quieter entries and they are often skipped. Water content in particular matters for lyophilised material, because moisture drives degradation over time. A high figure is a sign that the material may not hold up in storage.

Five things that invalidate a COA

1. The batch number does not match. The most common problem, and the most serious. A certificate for a different batch is a certificate for a different material.

2. There is no issuing laboratory. A legitimate certificate names the lab that produced it, on its own letterhead, with contact details. An unbranded PDF with a logo pasted at the top is not a lab report.

3. The lab is the supplier. In-house testing is not third-party testing. It may be perfectly competent, but the party with a commercial interest in the result is the one producing it. We cover this distinction in what "third-party tested" actually means.

4. There is no chromatogram. A percentage typed into a template can be typed by anyone. The trace is much harder to fake convincingly.

5. It only arrives on request, and then it doesn't. Suppliers with current documentation publish it. Suppliers who ask you to email for it are frequently buying time.

Why this is worth the five minutes

In July 2026, a pharmaceutical testing laboratory reported that close to 30% of peptide vials it tested from the open market came back with problems: mislabelled compounds, doses above or below what the vial claimed, and contamination with toxins or bacteria. The lab's co-founder described finding live or dead bacteria in a significant share of vials.

Nothing on a product page distinguishes those vials from sound ones. The certificate is the only thing that does, and only if you read it properly.

If you would rather work backwards from the supplier than the document, we have also written up the questions worth asking before you order.

Peplounge supplies research peptides for laboratory and educational research only. Not for human or veterinary consumption.