How to Read a Peptide Certificate of Analysis (COA): A Guide for Canadian Research Buyers
A Certificate of Analysis, or COA, is the single most useful document a Canadian research buyer can request before committing to a batch of peptide material. It is the manufacturer's signed record of what a specific lot actually contains and how pure it is. Reading one carefully turns a purchasing decision from guesswork into verification. This guide walks through every section you will meet on a typical peptide COA and shows how to cross-check the paper against the vial in front of you. You can see live examples on our certificates of analysis page.
The table below is a quick map of the fields a complete COA should contain and what a careful reader looks for in each one.
| COA field | What to check for |
|---|---|
| Product name and sequence | Matches the peptide you ordered and the wording on the vial label. |
| Expected vs found molecular weight | The theoretical and measured masses agree within a small tolerance. |
| HPLC purity (area percent) | Meets or exceeds the stated grade, such as ninety-nine percent and above. |
| Chromatogram | One dominant peak on a flat baseline with only minor satellite peaks. |
| Batch and lot number | Present and identical to the number printed on the vial. |
| Manufacture date | Recent enough that stability is not in question. |
| Test date | On or after the manufacture date and close to release. |
| Testing laboratory | Named, with the analytical methods referenced. |
| Appearance | Description matches the physical vial, such as a white lyophilized powder. |
Identity confirmation by mass spectrometry
The first job of a COA is to prove the vial holds the peptide named on the label and nothing else. Identity is confirmed by mass spectrometry, most often electrospray ionization paired with a mass analyzer. The report lists an expected molecular weight, the theoretical mass calculated from the amino acid sequence, alongside a found molecular weight measured from the sample. For a correctly synthesized peptide the two values agree closely, often within a fraction of a Dalton for a short sequence. A found mass that differs by the weight of a missing residue, an extra methyl group, or a bound acetate counterion is a signal to ask for clarification before the material goes anywhere near an experiment.
Purity by HPLC
Purity is measured by high performance liquid chromatography, usually the reverse-phase form. The column separates the intended peptide from truncated chains, deletion sequences, and leftover synthesis reagents, and a detector records each fraction as a peak. Purity is then reported as area percent: the area under the main peak divided by the total area of every peak, expressed as a percentage. When a COA states ninety-nine percent and above, it means the target peptide accounts for at least that share of the detected material. Higher purity means fewer unknown species competing in whatever assay the material is used for. Once purity is confirmed, you can plan concentrations with the reconstitution calculator.
Reading the chromatogram
The number alone can mislead, which is why the chromatogram itself belongs on the COA. A clean result shows a single tall, dominant peak sitting on a flat, quiet baseline, with any other peaks small and well separated. A trace with several large secondary peaks can still be dressed up with a high headline figure through selective integration, so the visual matters. A single dominant peak is the shape you want because it shows the mass and the purity both describe the same one compound.
Batch number, lot number, and dates
Every COA is tied to one specific production run through its batch and lot number. This is the thread that connects the paper to the powder. The manufacture date tells you how long the material has been in storage, and the test date tells you when the analysis was performed. The test date should fall on or shortly after manufacture, near the point of release. A COA with no lot number, or with dates that do not line up, cannot be matched to your vial with any confidence.
The testing laboratory
Finally, a COA should name the laboratory that ran the analysis and reference the methods used, such as the HPLC gradient and the mass spectrometry mode. Independent third-party testing, performed by a lab separate from the seller, carries more weight than an in-house sheet alone because the analyst has no stake in the result.
Cross-checking the COA against the vial
A COA only protects you if it belongs to the vial you received. Match the peptide name, match the lot number on the sheet to the number labeled on the vial, and confirm the described appearance against what you actually see. If any of the three fail to line up, treat the document as unverified. Before you buy, run through our quality checklist for researchers, and when you are ready, browse tested material in the store.
Research use only. This article is educational and is not medical, legal, or financial advice. The compounds discussed are not approved for human or veterinary use, consumption, or therapeutic application.