How to read a certificate of analysis

Almost every research peptide supplier publishes certificates of analysis now. That's an improvement over a few years ago, when most published nothing. But a COA is only useful if you read it, and most buyers glance at a purity figure and move on.

That figure is the least informative part of the document. Here's what the rest of it says.

What a COA is, and who writes it

A certificate of analysis is a report issued by a laboratory describing what it found when it tested a sample. It is a record of one test, on one sample, at one point in time.

The important word is issued. The lab writes the report. A supplier who retypes results into their own template, or summarizes them, has introduced a step where information can be lost or changed. What you want to see is the document the lab produced, with the lab's name on it.

If a supplier's COAs all look like they were made in the same design tool as the rest of their website, that's worth noticing.

The lines that matter

Identity

Confirms the sample is the compound named on the label, usually established by mass spectrometry measuring molecular weight against the expected value. This is the line everything else depends on — a purity figure means nothing if the wrong compound is 99% pure.

Purity

Typically measured by HPLC and reported as the compound's share of total peak area. Read that definition carefully. It describes how much of what the instrument detected was your compound, relative to everything else it detected. It is not a statement that the vial is 99% peptide by weight.

Net content

The actual measured mass in the vial against what the label claims. This is the figure skipped most often and it matters most in practice. A vial can be 99% pure and still contain meaningfully less material than labeled. Purity and quantity are separate measurements answering separate questions.

Lot or batch number

Ties the report to a specific production run. Without it, the report describes an unspecified quantity of material that may or may not be related to what you received.

Test date and method

The date tells you whether the report describes current inventory or something tested a year ago. The method — HPLC, LC-MS, and others — tells you what question was being answered. A report that doesn't say how a measurement was made is asking you to take the number on faith.

Matching the report to your vial

This is the step that separates a useful COA from a decorative one.

Find the lot number printed on your vial's label. Find the lot number on the certificate. They should match exactly.

If a supplier publishes one COA per product rather than one per lot, that report describes a batch someone received at some point — not necessarily yours. Manufacturing varies between runs. That is the entire reason lot numbers exist.

A supplier who can't tell you which report corresponds to your vial is publishing a document, not a record.

What purity figures don't tell you

A high purity number is good information with real limits.

It describes the sample submitted to the lab, not every vial in the batch. It describes what the instrument detected using that method, and a method that doesn't detect a given class of impurity won't report it. Residual solvents, endotoxins, and heavy metals each require their own tests, and a standard purity panel doesn't cover them.

None of this makes purity testing theater. It means a certificate answers specific questions and stays silent on others, and knowing which is which is the difference between reading a COA and looking at one.

Things worth a second look

• No lot number. The report can't be connected to anything you're holding.
• No lab named. You can't verify it, and neither can anyone else.
• No test date. The report could describe material from any point in the supplier's history.
• One COA covering an entire product line. Different compounds, same certificate, is not how testing works.
• A flattened image rather than a document. A screenshot of a report is harder to verify than the report.
• Every batch reporting an identical figure. Real measurements vary. A supplier whose every lot comes back at exactly the same number is either very lucky or not measuring.

Verifying independently

Most analytical labs will confirm whether they issued a given report. If a certificate names the lab and carries a report number, you can contact them and ask. Few buyers ever do, which is exactly why it's worth doing when something matters. Some labs also provide a verification portal where a report can be looked up directly.

How ours work

Batches we receive are sampled and sent to an independent lab. We don't test in-house. What the lab issues is what goes on the site — the same report, the same numbers, no summary in between.

Reports are organized by lot and stay published permanently, including previous batches, so a code printed on a vial a year ago still resolves to the report that described it.

Our current panel covers identity, purity by HPLC, and net content. We're expanding what we test for, and when we do, it will show up on the reports rather than in a marketing claim.

You can look up any lot number on our test results page.