Reading a Retatrutide Certificate of Analysis

Retatrutide is a lipidated, multi-receptor incretin analogue, and its certificates look different from those of a short unmodified peptide. This guide explains, field by field, what a retatrutide certificate reports, what is normal for this compound, and which figures to check before accepting a lot.

What is on the report

• Content per vial, in milligrams. Measured against a reference standard of retatrutide itself, usually on three separate vials from the same lot. This is the number that tells you how much peptide you actually have.
• HPLC purity, as a percentage, where the lot was tested for it. The share of UV-absorbing peak area eluting as the main peak.
• Endotoxin, in EU per vial, where a separate analysis was commissioned. It has its own report number and is not part of the purity run.
• Lot number and analysis date, which tie the report to physical material.

Why content usually reads higher than the label

A vial labelled 10 mg commonly reports 11 mg or more. This is normal: manufacturers overfill so that the vial still meets its nominal amount after fill-line losses, and the certificate reports what was measured rather than what was printed. What matters is that the measured figure is at or above the label, consistent across the three vials, and not wildly above it — a 10 mg vial reporting 15 mg suggests a filling problem, not a bonus.

Compare the three vial figures against each other. Tight clustering means a well-controlled fill; a spread of several milligrams means the lot is uneven and your own sample may sit anywhere in that range.

What lipidation changes

Retatrutide carries a long-chain fatty-acid group on a lysine side chain. For the analysis this matters in three ways:

• Retention time. The molecule is far more hydrophobic than a bare peptide, so it elutes late in a reversed-phase gradient and needs a high proportion of organic solvent.
• Peak shape. Lipidated peptides can self-associate, which broadens peaks. A slightly wider peak is expected here and is not by itself a sign of poor material.
• Quantification. Content must be measured against a reference standard of the lipidated molecule, because the lipid changes both UV response and chromatographic behaviour relative to the unmodified peptide.

Our guide on lipidated peptides covers the handling consequences in full.

Identity, and why purity alone is not enough

Purity describes how clean the main peak is. It says nothing about whether that peak is retatrutide rather than a related analogue — and the incretin family contains molecules of similar size and behaviour. Identity is confirmed by mass spectrometry, where the measured mass should match the expected mass including the fatty-acid chain. A result that matches the bare peptide mass, missing the lipid, is a different compound. See how mass spectrometry confirms identity.

The checks, in order

1. Does the lot number on the certificate match the number on the vial label?
2. Does the report resolve at the issuing laboratory, with the same figures? See verifying a report.
3. Are three vials reported, and how far apart are they?
4. Is purity reported for this lot, or carried over from an earlier one?
5. Is the chromatogram shown, or only a percentage? See reading the chromatogram.
6. If endotoxin is quoted, does it have its own report number and date?

Our retatrutide lots

We publish the Janoshik report for every retatrutide lot we ship — RT10 through RT60 — with content per vial for three vials, HPLC purity where it was tested, endotoxin where a separate analysis was run, and a link to verify each report at the laboratory. Where a lot has no purity figure, the page says so rather than reusing one from another lot. See the incretin and amylin analogues and the full results page.

Retatrutide is supplied for laboratory research use only. It is not a medicine and is not for human or veterinary use. This page describes analytical documentation only and makes no claims about biological effects.