The expanded version of this checklist is how to read a peptide COA (and spot a fake). Start there when you want the red flags for a reused, edited, or generic file. This page stays the short version.
You already know a percentage is the line people quote first. And you already know it is the line that tells you the least until the lot matches. When you open a certificate of analysis, start with the identifiers. The purity figure can wait.
A COA is a laboratory document about a specific sample. In research sourcing, it is how you check whether a seller's paperwork describes the container in front of you. It is a record of a test. It is not a performance promise, and it is not guidance for use in people or animals.
Match the document to the container
Imagine the label and the PDF in the same glance.
- The lot or batch number on the COA should match the lot printed on the vial or its label.
- The compound name on the report should match the name on the label. Salt forms, hydrates, and near spellings are not automatically the same material.
- A sample identifier, a receive date, and a report date show whether the file is tied to one shipment or reused across batches.
- The laboratory name, and an address or another traceable identifier, should appear on the report.
If the lot on the paperwork and the lot on the container differ, the document does not describe the container you have. Read that again before you go back to the percentage.
Read the test sections
Layouts vary. These sections show up often:
| Section | What to look for |
|---|---|
| Identity | A method the lab says supports the stated identity, such as mass spectrometry or a retention-time comparison. |
| Assay or purity | A chromatography result and the method name. Check whether the figure is area percent or a quantitative assay. |
| Appearance | Physical notes such as color or form. These are observations, not a quality conclusion by themselves. |
| Additional tests | Related substances, residual solvents, water content, counter-ion, metals, or microbial results, when the report includes them. |
A missing section means that test was not reported. It does not mean the untested property would have passed.
A single high purity percentage does not describe identity, and it does not describe contaminants that were never measured.
Third-party reports and in-house reports
As you notice who signed the file, keep the next distinction with it. An in-house report is produced by the seller or a laboratory the seller operates. A third-party report is produced by a separate laboratory. Outside paperwork is easier to weigh when you can tell who ran the test and which sample they received. A logo on a PDF is not the same thing as a traceable report.
Look for a method, a sample identifier, a date, and a laboratory identity you can look up. A cropped chromatogram with the header removed is harder to evaluate than a full report.
What a COA does not establish
- It does not establish that every vial in a catalog matches the tested sample.
- It does not establish that a later batch will match an older report.
- It does not establish that a material is appropriate for any use in humans or animals.
- It does not replace the method line. A percentage with no method is a marketing sentence until a report defines it.
PeptideRank's supplier list links a certificate page only when that page was open on the checked date. The quote is the supplier's sentence. Use the checklist above on the file itself.
For a closer look at independence, read how to evaluate a supplier's third-party testing.