How to read a certificate of analysis

A certificate of analysis, or COA, is a document that reports the results of laboratory testing on a specific batch of a product. For peptides, it is meant to show what is in the vial and how pure it is.

Most suppliers will show you a COA. Fewer people know how to read one. This guide covers the basics.

Who wrote it matters

The first thing to check is who did the testing. A COA can come from the manufacturer's own lab or from an independent third-party lab.

Third-party testing is generally more useful, because the lab has no direct interest in the result. Look for the lab's name, address and contact details. A real lab should be easy to find and should be able to confirm that it issued the report.

It should match your batch

A COA applies to one batch, sometimes called a lot. The lot number on the certificate should match the lot number on the product you receive. A COA for a different batch, or one with no lot number at all, tells you nothing about your vial.

Check the test date too. A report from several years ago may not reflect what is being sold now.

What to look for on the page

• Product name and lot number. These should match the label.
• Test methods. Common methods include HPLC, which measures purity, and mass spectrometry, which confirms identity.
• Identity result. This confirms the molecule is the one it claims to be, usually by comparing its molecular weight to the expected value.
• Purity result. Usually given as a percentage.
• Quantity or content. How much peptide is actually in the vial compared with what the label says.
• Contaminant testing. Some COAs include tests for endotoxins, heavy metals, residual solvents or microbes.
• Signature and date. A named analyst or reviewer and a clear date.

Why purity numbers alone mean little

Many listings lead with a single number, such as "99% pure". On its own, that number does not tell you much.

First, purity by HPLC tells you what share of the detected material is the main compound. It does not confirm that the main compound is the right one. That is the job of the identity test. A sample could be highly pure and still be the wrong molecule.

Second, purity does not tell you quantity. A vial labelled as containing a certain amount could contain much less, even if what is there is pure.

Third, purity does not cover everything that could be harmful. Endotoxins, for example, are fragments of bacteria that can cause reactions even in tiny amounts. They are not measured by a standard purity test.

Finally, a number is only as reliable as the lab and the document behind it. Edited or recycled COAs do exist.

Simple checks you can do

• Contact the lab directly and ask them to confirm the report.
• Compare the lot number on the COA with your product.
• Look for both identity and purity results, not just one.
• Ask whether endotoxin or sterility testing was done.
• Be cautious if a supplier will not share a full report.

The short version

A COA is useful, but only if it comes from a credible lab, matches your batch, and covers identity, purity, quantity and contaminants. A single high purity figure is a starting point, not proof of quality. If any of this is unclear, it is a good topic to bring to a consultation.