How to vet a peptide supplier: a 10-point checklist

How do I check a peptide supplier's certificate? (points 1 to 3)

Check three things on the certificate: that there is one for each lot, that it names the laboratory and who issued it, and what was tested.

1. One certificate per lot. A certificate of analysis describes one batch. A supplier that shows a single certificate for a product across every batch it has ever sold is showing you a sample, not the material you are buying. FDA's guidance for pharmaceutical ingredients, which does not govern research reagents but is a useful benchmark, expects a certificate for each batch, carrying the batch number and the date.

2. The named laboratory, and who issued the document. A certificate should name the laboratory that ran the analysis, and you should be able to tell whether that laboratory issued it or whether a supplier prepared it and names a laboratory. The same FDA guidance asks that a certificate reissued by an agent or broker name the laboratory that performed the analysis and reference the original. On this site, a certificate that reached us from a supplier, without the laboratory confirming it, is labelled "certificate supplied by" that supplier, "naming" the laboratory, rather than "assayed by" it.

Read the laboratory's own wording too. One laboratory on our certificates states on the document that the sample information "was submitted and certified by the client" and that it takes "no responsibility as to the accuracy" of it. That is a normal disclaimer, and it means the laboratory attests to what it received and measured, not to where the sample came from. Accreditation is a separate question: ISO/IEC 17025 is the international standard for the competence of testing laboratories, so ask whether the named laboratory holds it, and for what scope. Of the laboratories our certificates name, we state it only for ILS Laboratories, because that is the one we have it on record for.

3. What was tested. Purity, identity and safety screens are different questions. HPLC purity tells you how much of the sample is the main compound; it does not tell you that the main compound is the one on the label. Identity needs mass spectrometry or comparison against a reference standard. Endotoxin, sterility, microbial limits and heavy metals are further tests again. In US drug manufacturing, a company that relies on a supplier's report must still run at least one specific identity test of its own (21 CFR 211.84). Certificates on this site vary in exactly this way: some report HPLC purity with LC-MS identity, some add endotoxin and microbial limits, and our MOTS-c certificate reports purity by HPLC alone. HPLC vs mass spec: what each test proves explains the difference in more depth.

What should a certificate's numbers show? (points 4 and 5)

A certificate should print a measured figure rather than a minimum, for a lot you can match to the vial you receive.

4. Measured figures, not minimums. "≥99%" is a specification, a promise about a range. "99.59%" is a measurement of one lot. A certificate that prints only a minimum tells you the batch passed a threshold, but not by how much, and it makes two lots impossible to compare. The FDA guidance asks for each test's acceptance limit and the numerical figure obtained. Expect the occasional exception and judge it in context: one of our own certificates, for Selank, prints its purity as ">99.80%", and we show it exactly as printed rather than round it into a single number. Peptide purity: 98% vs 99% in practice covers what a point of purity does and does not mean.

5. Traceability to the vial you receive. The lot on the certificate should match the lot on your label or packing slip, and the supplier should be able to confirm the match when asked. Without that link, a genuine certificate proves nothing about your material. Where a laboratory offers online verification of its certificates, use it. Our COA library lists each certificate's lot, and we will confirm which lot an order received.

How does a supplier handle gaps and errors? (points 6 and 7)

Look for a supplier that shows you which products lack a certificate and corrects its errors in the open.

6. Honest gaps. Few suppliers hold a current certificate for every compound they sell, so the useful question is whether the supplier shows you which ones lack one. A catalogue in which every product claims testing, with no documents behind some of them, is a warning sign. On this site, a product without a certificate makes no claim about testing, and the COA library lists it as in progress. Our AOD-9604 page shows no certificate because our supplier publishes none for it, rather than borrowing one from a neighbouring product.

7. Public corrections. Certificates contain mistakes, and so do the sites that publish them. What matters is whether errors are corrected in the open. Three of our certificates print a molecular formula that does not match the compound's structure or the certificate's own molecular weight: IGF-1 LR3, MOTS-c and tesamorelin. Their certificate panels show the corrected formula, with the printed one and the reason beside it, and the document itself is left as issued. A supplier that quietly swaps a document, or never admits an error, gives you no way to know what else has changed.

What should the business behind it look like? (points 8 to 10)

The business should frame its products for laboratory research everywhere, publish policies that agree with each other, and have a real identity you can reach.

8. Consistent research-use framing. Product pages, terms, packaging, email and social posts should all say the same thing: the material is for laboratory research. A supplier that states research use only in its terms while hinting at personal use in its marketing is telling you its compliance is a formality, and that it may not last. Consistency here is also a sign of a business that expects to be around next year.

9. Policies that agree with each other. Shipping, refund and contact policies should be published, specific and consistent. If the refund policy promises one thing and the FAQ another, or delivery times differ between checkout and the policy page, assume the stricter reading will be the one applied to you.

10. A real business identity. Look for a named legal entity, a postal address and a working way to reach a person. Test it with a question about a certificate before you order, and see whether the answer is specific. Suppliers do close, sometimes without warning; Peptide Sciences shut down: how to choose an alternative shows how little a closure notice may say.

How should I use the 10-point supplier checklist?

Score suppliers against the tests your protocol needs, and keep the certificates for the lots you used with your lab records. No single point settles the question, and a supplier can pass most of them and still fail one that matters for your work. Identity testing matters more for some experiments than an endotoxin screen, and the reverse is true for others.

For the certificate itself, How to read a peptide certificate of analysis walks through each field, and Red flags in a peptide COA: spotting a fake lists the signs of a certificate that should not be trusted. Our testing page shows what each of our certificates reports, grouped by the laboratory it names.

Sources

1. FDA, Q7 Good Manufacturing Practice Guidance for Active Pharmaceutical Ingredients, Guidance for Industry (Revision 1, September 2016), sections 11.4 and 17.6 (fda.gov, source 1, accessed October 20, 2026)
2. 21 CFR 211.84, Testing and approval or rejection of components, drug product containers, and closures (eCFR) (ecfr.gov, source 2, accessed October 20, 2026)
3. ISO, ISO/IEC 17025: Testing and calibration laboratories (iso.org, source 3, accessed October 20, 2026)