Tirzepatide lab tests

Seven checks before you trust a Tirzepatide certificate

The same seven questions decide whether a certificate of analysis means anything, whichever compound it describes. Six are about the document; the seventh is about what no document can tell you.

1. An independent, batch-matched COA. The certificate must name the batch or lot in your hands, and must come from a laboratory the vendor neither owns nor pays. A specimen certificate from an earlier lot proves nothing about the vial you were sent.
2. HPLC purity, read against a known band. A purity figure is only informative against the distribution for that compound. "Above 98%" is not a claim — the useful question is whether the result sits inside the range the rest of the market reports. How to read HPLC and mass-spec results.
3. Mass-spectrometry identity. HPLC says how much of the sample is one thing; it does not say which thing. Only a mass-spec result establishes identity, and it is the only check that separates compounds a few daltons apart. Contamination is not hypothetical: research-grade custom peptides from two independent commercial suppliers were found to carry contaminating peptides at roughly 1% by weight, enough to produce false-positive results in immunology assays (Clinical and Vaccine Immunology, 2008 — a study of HIV vaccine peptide libraries rather than of any compound on this site).
4. Net content, measured rather than assumed. Purity and quantity are different questions: a vial can be 99.7% pure and still contain two thirds of the labelled mass. Why 10 mg isn't 10 mg.
5. Endotoxin (LAL) on the batch. An absent endotoxin line means the batch was not tested — not that it passed. Endotoxin testing and LAL interpretation.
6. Who ran the test, and what they left off. A laboratory with a record on this compound, named on the certificate, with a verification route back to it. Testing laboratories we track · Red flags in a certificate of analysis.
7. What no test on the vial can establish. A perfect certificate confirms that a vendor sold the correct molecule at the stated quantity. It says nothing about efficacy, dosing, or long-term safety.

Want a vial tested yourself? How to send a peptide for independent HPLC testing.

What tirzepatide testing has to rule out

Tirzepatide is a 39-residue synthetic peptide with a C20 fatty diacid moiety, acting at both the GIP and GLP-1 receptors: CAS 2023788-19-2 (PubChem CID 156588324), formula C₂₂₅H₃₄₈N₄₈O₆₈, molecular weight 4,813.0 g/mol, development code LY3298176. The diacid makes it a peptide-lipid conjugate rather than a simple synthetic peptide, and the conjugation chemistry is a manufacturing step grey-market synthesis can get wrong. Incomplete acylation produces material that elutes convincingly and reports a respectable purity figure while sitting at the wrong mass, so the mass-spectrometry result has to be 4,813.0 Da with the C20 diacid attached. Semaglutide sits at 4,113.6 g/mol.

On this compound the documented failure is quantity rather than identity. Across 930 independent lab tests on this platform (verified August 2026), purity averaged 99.75% while fill quantity ran from +2.6% to +26.7% against the label: vials labelled 10 to 65 mg tested between 10.71 and 68.1 mg. The deviation on record runs in one direction — more drug in the vial than the label claims — so the milligrams paid for and the milligrams in the vial are different numbers. That is why quantitative content testing comes first on tirzepatide.

FDA has stated that salt forms of these peptides "are different active ingredients than are used in the approved drugs", and the same logic applies to any tirzepatide salt; a certificate that omits the form has omitted what is being weighed. LAL endotoxin results are the routinely skipped line on GLP-1 certificates.

• Quantitative content testing on the batch: +26.7% over label is on record.
• Mass spectrometry at 4,813.0 Da with the C20 diacid attached — HPLC purity alone cannot detect incomplete acylation.
• The salt form stated on the certificate.
• An LAL endotoxin result on the batch rather than a field blank.