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How to read a peptide COA: each line, and what it ties to
How to read a peptide COA line by line: what identity, purity, quantity and endotoxin results show, and what a vendor or anonymised COA ties them to.
To read a peptide COA, start with the sample block: product, stated amount, vendor name and batch ID, or a third-party record ID. Then take each result line on its own terms. Mass spectrometry confirms identity, HPLC-UV gives purity, an HPLC assay gives quantity, and endotoxin and heavy-metal lines report contaminants the purity figure cannot see.
This is an evergreen guide on how to read a peptide COA, and it sits at the centre of this desk’s COA coverage. The working source is Finnrick’s guide, How to read a Certificate of Analysis (COA), dated 1 March 2026, which this desk read on 3 October 2026. Finnrick is a testing service. Its positions below are attributed to it as its own, and nothing here assesses the quality of its testing.
How to read a peptide COA, section by section
A COA is a lab’s report on one sample. Finnrick’s guide says it covers the specific sample submitted and does not verify what vendors sell in other batches or shipments. Every line below carries that scope.
Sample information: what was tested
The top block names the product, the stated amount (the label claim), the vendor name and batch or lot number, the date the lab received the sample and a description. Finnrick’s guide treats the vendor and batch lines as critical. Its verdict on a vendor-supplied COA that lacks them: “entirely worthless and should be ignored altogether”.
What does each result line measure?
| Line | Method named in Finnrick’s guide | What it reports | What it does not show (this desk’s reading of the method’s scope) |
|---|---|---|---|
| Identity | HPLC/MS | Molecular weight matches the expected compound | Purity |
| Purity | HPLC-UV, around 214–220 nm | Expected peptide’s share of UV-detectable peptide signal, as % | Salts, fillers, excipients, water, endotoxin, metals |
| Quantity | HPLC assay against a reference standard | mg in the vial and % of label claim | A weighed mass |
| Endotoxin | LAL or recombinant assay | EU/mL, EU/mg or EU/sample, or detected/not detected | Peptide identity, purity or quantity |
| Heavy metals, if tested | ICP-MS | Lead, arsenic, cadmium, mercury | Endotoxin or peptide content |
Only the purity row’s exclusions are stated by Finnrick; the other exclusions are this desk’s inference from what each method measures.
Purity is the line most easily over-read. Because it counts only peptide-related signal, a high figure is not a net-content figure. Does 99% purity mean 99% peptide by weight? works through that gap, and the TFA vs acetate post covers the counterion line that often explains part of it.
Identity is a separate question. Per the guide, a failed identity line can mean a different peptide, a blend, degradation fragments or no peptide at all. What MS confirms that HPLC purity cannot sets the two methods against each other.
Quantity is an estimate. The guide says it is calculated against a reference standard, not measured by weighing the peptide.
Vendor-supplied COA vs anonymised third-party COA
The same result lines can sit on two different kinds of document. What changes is what the result is tied to.
| Field | Vendor-supplied COA | Anonymised third-party COA (Finnrick’s model) | ECA summary of EU GMP Part II 11.4 |
|---|---|---|---|
| Vendor name | Should name the exact vendor | Most do not carry it | Name of the company or laboratory |
| Batch ID | Should carry one | Most do not carry it | Batch number |
| Sample identifier | Batch or lot number | Finnrick Record ID, matchable at finnrick.com/verify | Name of the intermediate or API |
| Scope | The sample tested | The sample tested | Each batch |
| Dates | Not stated in the sources read | Date received by the lab | Release date and expiry date |
| Tests | Methods and results | Methods and results | Tests with acceptance limits; numerical results |
| Sign-off | Not stated in the sources read | Lab, technician signature, date | Dated signature by authorised personnel |
Finnrick’s guide says most of its own COAs omit vendor and batch because samples are anonymised before they reach the lab, to mitigate conflicts of interest. A vendor COA with a batch ID ties a result to a production run as the vendor labels it. An anonymised COA ties it to a sample record. Neither, on its own, shows what is in a given shipment. How to verify a peptide COA is real covers checking the document itself.
The right-hand column is the ECA Foundation’s 2017 summary of COA requirements, which says section 11.4 of the EU GMP Guide Part II asks for an authentic certificate for each batch of an intermediate or API. This desk read that summary on 3 October 2026, not the guide’s own text. Those rules govern manufacturers of intermediates and active pharmaceutical ingredients. They are a reference for what a complete certificate looks like, not a standard research-use sellers are held to, and nothing here says any vendor or lab meets them.
Frequently asked questions
What should a peptide COA include?
Finnrick’s guide says it requires identity confirmation, purity and quantity, with potential contaminants as a possible addition. Around those results, a usable COA names the product, the stated amount, the vendor and batch ID or a third-party record ID, the methods used, the lab, a signature and a date. A result with no sample identification attached says little about any vial.
How do you know if a peptide COA is legit?
Start with the link between the document and the product. A vendor-supplied COA should carry the vendor’s exact name and a batch ID that matches the vial; Finnrick’s guide says one without them should be ignored. An anonymised third-party COA should carry a record ID that can be matched on the testing service’s own site. Checks on the document itself come after that.
What is the difference between HPLC and mass spec on a COA?
HPLC with UV detection reports purity: the expected peptide’s share of the UV-detectable peptide signal. Mass spectrometry confirms identity, by checking that the molecular weight matches the expected compound. Finnrick’s guide notes that UV purity does not on its own confirm molecular identity, and that MS verifies mass rather than estimating purity. A COA needs both lines to say what the material is and how clean it is.
A COA is a document about a sample, and this desk reads it as one: what was tested, by which method, tied to what. Research peptides are supplied for laboratory research use only. Nothing here is medical advice, no compound discussed is intended for human consumption, and this desk does not publish dosing.