What a COA is
A COA is a document from a testing lab that reports results for one production batch, called a lot. It usually covers identity, confirmed by mass spectrometry, and purity, measured by HPLC. Some also report the amount measured in the vial, endotoxin, sterility, heavy metals or leftover solvents. A COA describes the sample the lab received. It is evidence about that lot, not a guarantee about every vial, and it is only as good as the lab behind it.
The parts of a COA, line by line
- Product name and ID
- The compound's name, often with its sequence or CAS number, a registry number for one specific substance. Both should match the vial's label.
- Lot number
- The batch code. It should match the lot printed on the vial, because a report for a different lot says nothing about the one in hand.
- Test date
- When the lab ran the tests. It should fit the lot: after the batch was made and reasonably recent, not a years-old report reused across batches.
- Identity by mass spectrometry
- Mass spec measures the weight of the molecule. The report should show the measured value next to the expected molecular weight, and the two should agree closely.
- Purity by HPLC
- HPLC separates the sample into its parts and reports the main peak as a percentage of everything the detector saw. This is the purity figure most COAs lead with.
- The chromatogram
- The HPLC graph: one large peak for the peptide and small peaks for impurities, usually with a table of each peak's area. It is what makes the purity number checkable.
- Amount (quantity)
- Some labs report how many milligrams they actually measured. This matters for lab math: if a vial labeled 5 mg holds 4 mg, every concentration worked out from the label is off.
- Lab name and independence
- The lab's name and contact details. A third-party lab carries more weight than the seller's own letterhead, and ISO/IEC 17025 accreditation means an outside body has assessed its competence for the tests it lists.
- Endotoxin and sterility
- Endotoxin testing, usually by the LAL method, looks for bacterial fragments that can cause fever and inflammation, while sterility testing looks for living bacteria and fungi. They are separate tests, and many COAs include neither.
- Heavy metals and solvents
- Some reports also test for metals such as lead, arsenic, cadmium and mercury, often by ICP-MS, and for solvents left over from manufacturing.
How identity and purity fit together
Identity and purity answer different questions, so a complete COA shows both. Mass spec confirms that a molecule of the right weight is present, but not how much of the sample it makes up. HPLC shows how clean the sample is, but a single tall peak could in principle be the wrong compound. Some labs run the two together, called LC-MS, so each peak is both measured and identified. HPLC purity is also not net peptide content: the powder holds water and salts that HPLC doesn't count, so 99% HPLC purity is not 99% peptide by weight.
Red flags
- No lot number
- A report that can't be tied to a batch can't be tied to the vial.
- No lab named, or only the seller's letterhead
- Without a named outside lab there is no one to confirm the result with.
- Dates that don't line up
- A test date before the lot was made, or years older than the batch, suggests the report belongs to something else.
- Purity shown without a chromatogram
- A percentage on its own can't be checked.
- Purity of exactly 100.0%
- Real HPLC results almost always show some small impurity peaks.
- The same COA for different lots
- Each batch should have its own report, with its own lot number and test date.
- A lab that can't be contacted
- With no website, contact details, report ID or lookup page, there is no way to confirm the report with the lab.
- Blurry, cropped or edited-looking files
- Mismatched fonts, covered fields or missing pages are reasons for caution.
What a COA can't prove
Even a genuine, verified COA has limits. It describes the sample the lab tested, not necessarily every vial in the batch, and says nothing about how vials were stored or shipped afterward. Beyond the matching lot number, it can't show that a given vial came from that batch. A mass match confirms weight, not always the order of the amino acids. And purity is not safety: a COA is not evidence that a compound is safe or effective for any use.
A checklist to keep
Matthew's free reader kit includes a one-page COA checklist in the same order as this guide: is it for this vial, who tested it, what they tested, and the red flags. The peptide glossary defines HPLC, mass spec, endotoxin and the other terms on a report. When a COA gives a measured amount, the calculator shows how a different number of milligrams changes the concentration.
