Semaglutide lab tests

Seven checks before you trust a Semaglutide 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 semaglutide testing has to rule out

Semaglutide is a 31-amino-acid analogue of human GLP-1(7-37) — Aib at position 8, Arg34, and a C18 fatty-diacid on Lys26 via a γGlu/OEG linker — CAS 910463-68-2 (PubChem CID 56843331), formula C₁₈₇H₂₉₁N₄₅O₅₉, molecular weight 4,113.6 g/mol, development codes NN9535 / NNC 0113-0217. It is not built on an exendin-4 backbone; that is the scaffold of exenatide, a different drug, and a product page repeating the exendin-4 lineage has copied its chemistry from the wrong molecule. "GLP-1SG" is a catalog code for semaglutide, not a separate or cheaper compound.

The molecule is easy to identify by mass, so the failures that actually occur are substitution of a salt form and quantity that does not match the label. FDA has stated that semaglutide sodium and semaglutide acetate "are different active ingredients than are used in the approved drugs", and that the agency "does not have information on whether these salts have the same chemical and pharmacologic properties." A vial of a salt form can return a genuine 99% HPLC purity figure — of something no randomised trial has tested. A salt form also changes what is being weighed: a labelled 10 mg can be 10 mg of a salt of which the peptide itself is some smaller fraction. Neither effect is visible on a purity percentage; both are visible on a certificate that states the form, and both are resolvable by mass spectrometry plus a net-content measurement.

Tirzepatide, sold alongside it, sits at 4,813.0 g/mol (CAS 2023788-19-2). The distance between 4,113.6 and 4,813.0 is why mass spectrometry is not optional: HPLC reports what proportion of the sample is the main peak, not which molecule that peak is.

• Mass spectrometry near 4,113.6 Da, confirming the 31-residue analogue with its C18 diacid attached and separating it from tirzepatide at 4,813.0 Da, from fragments, and from a peptide that merely elutes in the right place.
• The salt form — free base, sodium or acetate — written on the certificate. "Pharmaceutical grade" does not answer the question.
• Net peptide content or amino acid analysis, reported separately from purity.