Reading a Tirzepatide Certificate of Analysis

Tirzepatide certificates follow the same structure as other lipidated incretin analogues, but there are two things worth understanding before reading one: what the measured content figure is actually telling you, and why an endotoxin number on the same page is a separate test with separate limits.

The three numbers

• Content per vial (mg). Quantified by HPLC against a reference standard of tirzepatide, normally on three vials from the lot. Expect figures at or modestly above the nominal label weight.
• Purity (%). The main peak’s share of integrated UV-absorbing peak area. For a well-made lot this sits in the high nines; see what the purity figure actually measures before reading much into the decimal places.
• Endotoxin (EU/vial). Only where a separate analysis was commissioned. It is a bacterial-contamination measure for that lot, carries its own report number, and says nothing about sterility.

Why the label weight and the measured content differ

The powder in the vial is tirzepatide plus counter-ions plus residual water. The certificate’s content figure is the peptide itself, measured against a standard — which is why it is the number to base any calculation on, not the weight printed on the label. Our guide on net peptide content explains the gap, and counter-ions explains where part of the extra weight goes.

Three vials reported close together indicate an even fill. A wide spread means the lot varies, and the vial you receive could be at either end.

What the fatty-acid chain means for the analysis

Tirzepatide carries a C20 diacid chain on a lysine side chain. The practical consequences in the laboratory are the same as for other lipidated peptides: late elution in reversed-phase gradients, broader peaks from self-association, adsorption losses at low concentration, and quantification that must use a standard of the lipidated molecule rather than the bare peptide.

For identity, the measured mass must include the lipid. A mass matching the unmodified backbone is a different molecule, however good the purity figure looks.

Reading the endotoxin line correctly

Where a lot has been tested, the figure is reported as endotoxin units per vial — for example “<1 EU/vial” or “3.795 EU/vial”. Two points are routinely misread:

• It is not a sterility result. A lot can be low in endotoxin and still carry viable organisms, and vice versa.
• It describes that lot only, from its own analysis with its own report number and date. An endotoxin figure quoted without a report number cannot be checked.

See endotoxin testing, and what EU per vial actually means.

Checks before accepting a lot

1. Lot number on the certificate matches the vial label.
2. The report resolves at the issuing laboratory with the same figures — how to check.
3. Content reported for three vials, clustered rather than scattered.
4. Purity measured on this lot, not carried over.
5. Chromatogram shown, not just a percentage.
6. Endotoxin, if quoted, has its own report number and date.

Our tirzepatide lots

T12, T30 and T60 each ship against a Janoshik report published on the product page and on the lab results page, with content for three vials, HPLC purity, endotoxin where tested, and a verification link to the laboratory’s own record. Figures appear as reported, including the lowest vial.

Tirzepatide 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.