Purity, Potency, Identity: Not Synonyms

ON THIS PAGE

1. Key findings
2. Purity: how much of the peak is the target, by one method
3. Identity: which molecule, not how much of it
4. Potency: how much of the labeled amount actually got there
5. What a bare percentage does not tell a buyer
6. Limitations and open questions
7. Sources

A supplier that advertises a bare purity percentage and calls it third-party tested has told a buyer almost nothing about how much of the vial is the compound at all. Purity, identity, and potency are three separate measurements, made by different methods, against different standards, and a certificate that reports one has answered none of the other two.

Purity: how much of the peak is the target, by one method

This publication's explanation of HPLC purity covers the mechanics in full: a chromatographic run separates the components of a sample by retention time, and purity is the percentage of the detected peak area attributed to the target compound against everything else the method also separated out. Luxara Labs' 10mg retatrutide certificate, read 2026-08-25, prints the sharpest version of this limit in the document's own words: chromatographic purity "bounds peptide-related impurities only, not excipients, counter-ions, or residual water," a citation to Ph. Eur. 2.2.46 sitting beside the number. A purity figure says what fraction of the peaks the method saw belongs to the target molecule. It says nothing about how much of the vial's total mass that molecule actually is.

Identity: which molecule, not how much of it

This publication's piece on mass spectrometry covers why identity is a different question again: a mass measurement confirms that the molecule present matches the one claimed, independent of what fraction of the sample it makes up. An FTIR spectrum answers that same question by a different route. Several certificates in this ledger carry an FTIR line confirming the compound's presence while stating, in the same clause, that the analysis found it "with addition of excipient(s)/fillers," wording that appears on documents published by Excalibur Peptides, Chimera Peptides, and Noble Chems, read between 2026-08-24 and 2026-08-26. That line answers identity. It does not answer how much of the finished vial the confirmed molecule accounts for, which is the question potency exists to answer.

Potency: how much of the labeled amount actually got there

Potency is an assay measuring the quantity of active compound a sample delivers against a reference standard, reported as a percentage of the label claim. It is the number that would tell a buyer whether a 10mg vial actually contains 10mg of active compound once excipients, moisture, and manufacturing variance are accounted for, and it is the rarest of the three figures in this ledger. Of 126 supplier records, four hold a certificate line naming a distinct potency assay in those words, separate from the purity figure on the same document: Excalibur Peptides, Chimera Peptides, Noble Chems, and Vertex Labs. That four is a count of records, not of certificates. One of the four publishes a library of 35 certificates, read 2026-08-24. Three of the four name the chapter the potency figure was read under, USP General Chapter <621>, on the line the figure sits on. The Chimera Peptides document quoted below does not, though the chapter is printed on that vendor's 40mg certificate.

Those four documents are worth reading closely, because the number they report can look reassuring while the document beside it says something different. Vertex Labs' certificate for its retatrutide 10mg benchmark lot, read 2026-08-24, reports potency at 105.1 percent of the 10mg label, over label rather than under it, while the same document discloses a peptide-to-excipient ratio of 1 to 6.7, a number the certificate states plainly rather than hides: most of the vial's 81.3mg total mass is excipient, not the peptide the potency figure describes. The 10mg certificate Chimera Peptides publishes reports potency at 103.3 percent of label alongside an FTIR line naming mannitol, a lyophilization bulking agent, disclosed on the same page. The certificate Noble Chems publishes reports 104 percent of label with its own excipient ratio printed beside it, 10.4mg of peptide against 83.5mg of excipient. Three of the four, the Excalibur Peptides, Chimera Peptides, and Noble Chems documents, name a third party, Finnrick, in the Customer field rather than the storefront that publishes them, which is why this piece calls them documents these vendors publish rather than documents naming them as the customer. None of these documents conceals the excipient mass. They print it, in the same USP-numbered format as the potency figure, and a reader who checks only the percentage misses the ratio sitting next to it.

What a bare percentage does not tell a buyer

A certificate carrying purity alone has not told a buyer whether the vial contains the claimed molecule at all, only that whatever it does contain is mostly one thing by one method's accounting. A certificate carrying identity alone has confirmed the molecule without saying how much of it is present. Neither substitutes for potency, and potency itself, on the four documents quoted above, still needs the excipient ratio read alongside it to mean anything close to "10mg of compound in this vial." Luxara Labs' separate "label accuracy" figure, measured at 103.2 percent and 109.4 percent on two different lots read the same day, functions as a rough proxy for potency without using the word, and it carries the identical limitation: a label accuracy figure over 100 percent says the net peptide content exceeded the specification, not that the ratio of peptide to everything else in the vial matches what a buyer might assume from a bare percentage.

Limitations and open questions

The four-record count for a named potency assay is a substring search over ledger/vendors.json run on 2026-09-18, for the exact phrase "potency assay" or "Content/Potency" in a certificate context; a broader search for any figure functioning as a potency proxy under a different name, such as Luxara Labs' label accuracy, would return a different and larger number, and this piece does not claim to have found every such proxy across all 126 records. Each named certificate was read on the date given between 2026-08-24 and 2026-08-26, and a supplier's current documentation may differ from what was recorded then. This piece takes no position on whether any of the four named suppliers' potency figures are accurate measurements, only on what the documents themselves state about scope and method, since that is what the certificate makes checkable and the underlying assay is not.

Three words, three different questions, and most certificates in this ledger answer only the first one. The other two are worth asking for by name.

Sources

Supplier observations are this publication's own, from the dossier record in ledger/vendors.json: Luxara Labs and Vertex Labs, both read 2026-08-25 and 2026-08-24 respectively; Excalibur Peptides, read 2026-08-24; Chimera Peptides, read 2026-08-25; and Noble Chems, read 2026-08-26. The mechanics of purity and identity are covered in more depth in this publication's own linked pieces, each carrying its own sources. Vendors are named here, never linked, per site policy.