HPLC Purity on a Peptide COA, Explained

The HPLC purity percentage on a certificate of analysis tells you what fraction of the material in the vial is the peptide named on the label, and what fraction is something else — an incomplete synthesis fragment, a residual salt, moisture, or a different peptide entirely. It is not a marketing claim and it is not a one-time rating for "the product": it is a laboratory measurement of one specific manufacturing lot, tied to a report number and a date.

What HPLC actually measures

HPLC stands for high-performance liquid chromatography. A dissolved sample of the peptide is pushed under pressure through a column packed with material that retains each component differently, mostly according to how hydrophobic it is. The amino acid hydrophobicity scale described by Kyte and Doolittle in 1982, still the standard reference in the field, is what determines how long each fragment stays on the column before it elutes. A detector at the outlet records how much material comes through over time, producing a chromatogram made of peaks — each peak is a distinct compound, and the area under it is proportional to how much of that compound is present.

If the synthesis went well, the largest peak corresponds to the labeled peptide. Purity is that peak's area divided by the total area of every peak detected. A certificate reading 99.7% means the remaining 0.3% of detected material is something else — typically a leftover from the chemical synthesis process, not microbial contamination.

What a certificate of analysis actually shows

A peptide certificate of analysis (COA) normally lists the compound name, a lot number, the date of testing, the labeled content in milligrams, the actual measured content, and the HPLC purity percentage. These are figures for one specific manufacturing lot, not a general statement about "the product line."

As a concrete reference point: the independent lab Janoshik Analytical tested a retatrutide lot labeled at 10 mg on 2026-04-13 and reported 11.96 mg of actual content at 99.893% HPLC purity. The same day it tested a MOTS-c lot and reported 11.31 mg of content at 99.669% purity. That 99.669% figure is the lowest purity value published across PeptoClinic's reports so far, and it is the one worth citing if someone asks "what's the real floor," rather than quoting the best number on file.

Both of those are sold research peptides. PeptoClinic's catalog page for retatrutide and for MOTS-c link to the underlying reports.

Does an HPLC number stand on its own?

HPLC purity answers one question: how much of the detected material is the main peptide peak versus other substances absorbing at the same wavelength. It does not confirm exact molecular weight — that typically takes mass spectrometry — and it does not say how much residual water or salt is left in the lyophilized powder, which is measured separately. A complete report combines more than one method: the milligram content figure comes from the sample's absorbance, converted using a molar absorption coefficient specific to that peptide's amino acid composition, as described by Pace and colleagues in 1995. Two lots with the identical HPLC purity percentage can report different real milligram counts if their sequences differ, because the two numbers come from different measurements, not from one being derived from the other.

Put plainly: HPLC purity tells you how clean the main peak is. Milligram content tells you how much of that peak you have. A report worth reading shows both figures, not just the percentage. That is one of the first things to check on PeptoClinic's quality page before buying from any supplier.

How to verify a certificate belongs to the lot in hand

A certificate with no way to check it is, in practice, just an image file. What makes it checkable is that the laboratory that signed it runs a public system for looking up a report by lot number or report key, independent of the seller. Janoshik Analytical publishes each report under its own identifier — task numbers 136921 and 136923 in the examples above — searchable directly on the lab's own site, with no need to trust a screenshot forwarded by a vendor.

Two simple questions separate a real certificate from a decorative one: does the laboratory that signed it exist as a named, independently reachable organization, or is it just a logo someone drew? And does the lot number on the certificate match the one printed on the vial that actually arrived? If the answer to either is "I don't know," the certificate is not doing its job.

Does 99% purity mean "approved for human use"?

No. HPLC purity measures the chemical composition of the vial's contents relative to other chemical species — it does not evaluate sterility, does not test for endotoxins, and carries no regulatory meaning. None of the compounds in PeptoClinic's catalog, including retatrutide, MOTS-c, GHK-Cu, or BPC-157, is approved by the FDA. Retatrutide specifically is in phase 3 clinical development for obesity and type 2 diabetes, per Jastreboff and colleagues, New England Journal of Medicine, 2026; the others have no public approval timeline. A high purity figure describes the analytical quality of that lot. It says nothing about the regulatory status of the molecule itself.

PeptoClinic is a clinic: a physician reviews each consultation before anything ships, and the certificate for the relevant lot is viewable on the product page before a reader goes any further.