What 99% Purity Means in a Peptide

The purity percentage in a peptide indicates what fraction of the sample is the target molecule, measured as the percentage of peak area attributed to the main compound in an HPLC chromatogram. A result of 99% means that 99 out of every 100 units of detected area correspond to the peptide of interest. The remaining 1% is everything else: truncated sequences, oxidized forms, residual synthesis salts, and other byproducts.

That 1% matters in research. A sample labeled at 95% purity contains five times more uncharacterized material than one at 99%. When an experiment yields an unexpected result, the question "could the impurity have contributed?" is much harder to rule out in the less pure sample.

How HPLC calculates purity

The instrument injects a known quantity of the sample into a column packed with a stationary phase. A solvent flow carries it forward. The different molecules in the mixture interact with the stationary phase at different strengths, so they travel at different speeds and emerge from the column separated.

An ultraviolet detector — typically at 220 nm for peptides — measures how much signal each fraction produces as it exits. The result is a chromatogram: a plot of time against absorbance, with one peak per compound present in the sample. Purity is calculated by dividing the area of the main peak by the total area of all peaks combined.

The method has one limit: it does not distinguish between molecules that absorb similarly at 220 nm. For that reason, reference analytical laboratories combine HPLC with mass spectrometry to confirm molecular identity. The chromatograph separates; the mass spectrometer identifies.

What can be in that remaining percentage

In a synthetic peptide, the material that is not the target molecule can include:

• Truncated sequences: peptides missing one or more amino acids because the synthesis did not complete every coupling cycle. These may have a different biological profile from the full compound.
• Oxidized forms: amino acids such as methionine or cysteine oxidize if the purification process or storage conditions do not adequately control the environment.
• TFA salts: trifluoroacetic acid used in solid-phase synthesis remains as a counterion and may not be fully removed during purification.
• Residual moisture: in a lyophilized powder, water contributes to the mass of the vial but is not counted in the HPLC purity figure, so the actual peptide content may differ from the nominal label weight.

Why the number alone is not enough

A label that says "99% purity" is a starting point, not a verifiable claim. What matters is who analyzed the sample, using what method, and whether the report can be checked independently.

Two laboratories can report "99%" while measuring different things. If one uses HPLC at 254 nm and another uses 220 nm with confirmatory mass spectrometry, the numbers are not comparable even when they happen to be equal. A useful certificate of analysis includes the laboratory name with a task identifier, the wavelength and method used, the complete chromatogram, and a mechanism to verify that the report exists in the laboratory's own system.

PeptoClinic publishes the certificate of analysis for each lot in the quality section of the site. All reports are issued by Janoshik Analytical, a Czech laboratory that specialises in research peptides.

What the published reports show

All four certificates published by PeptoClinic were analyzed on April 13, 2026 by Janoshik Analytical. Two of them state the HPLC purity explicitly:

The retatrutide lot, task 136921, returned 99.893% purity. The vial was labeled 10 mg; the actual measured content was 11.96 mg — the difference reflects the weight of TFA salt incorporated in the lyophilized powder.

The MOTS-c lot, task 136923, returned 99.669% purity. Actual content: 11.31 mg.

The lowest purity figure published is 99.669%. That is the documented floor, not the laboratory's best result. A supplier that only cites its best lot is not being transparent. One that publishes every lot — including those at 99.6% — exposes the full track record.

The retatrutide and MOTS-c reports carry a working verification link to the Janoshik Analytical website. The other two — GHK-Cu and BPC-157 + TB-500 — contain a task key but no working link, because the laboratory's verifier returns an error when opened. That is documented and no link is provided to a broken page.

How to verify a certificate of analysis yourself

Any CoA, from any supplier, can be checked with these steps:

• Find the laboratory independently. Do not use the link the supplier gives you. Search the laboratory name, navigate to the site directly, and find the verifier there.
• Enter the task number. Most analytical laboratories have a page where you can type in the report identifier and confirm that it exists in their system.
• Compare the data. The compound, the purity figure, and the date shown by the verifier must match exactly what the document states. Any discrepancy invalidates the CoA.
• Check the stated method. A complete report names the column, the wavelength, and the solvent gradient. If it only says "HPLC: 99%", it is a number without analytical backing.

A supplier that delivers a CoA with a verifiable laboratory identifier is exposing their lot to external scrutiny. That is harder to fabricate than any badge displayed on a web page.

This material is for laboratory research only

The peptides that PeptoClinic Research Supply provides are strictly for research use only (RUO): in vitro experiments and laboratory work.

None of these compounds is a medicine, a supplement, or a food. None has received approval from any regulatory authority — FDA, ANMAT, or equivalent — for use in humans or animals. PeptoClinic Research Supply is not a pharmacy, not a clinic, and not a source of administration protocols or dosing guidance. No prescriptions are issued and requests for human-use protocols are declined.

If your research programme requires a compound from the catalogue, you can request a written quote specifying purity, quantity, and lot documentation.