TB-500 lab tests

Seven checks before you trust a TB-500 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 TB-500 testing has to rule out

TB-500 is a synthetic seven-residue fragment, Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln (Ac-LKKTETQ), CAS 885340-08-9 (PubChem CID 62707662), formula C₃₈H₆₈N₁₀O₁₄, molecular weight 889.01 Da. It corresponds to residues 17–23 of thymosin β4, a 43-amino-acid endogenous protein (CAS 77591-33-4, formula C₂₁₂H₃₅₀N₅₆O₇₈S, 4,963.44 Da, UniProt P62328), and is formally designated Ac-Tβ4(17-23). The two are sold interchangeably under both names, which is why this platform keeps them on separate compound pages, so that certificates for one molecule are not pooled with the other.

The masses differ by 4,074 Da — far easier to resolve than the 16 Da separating other commonly conflated pairs — so any mass spectrometer shows which molecule arrived, and there is no technical excuse for a vendor not knowing which compound it is shipping. A certificate reporting only a purity percentage has said nothing about identity.

Most research cited on TB-500 product pages was done on the parent protein. A 2026 scoping review included 80 studies, of which 70 were on thymosin β4 and exactly one was a direct TB-500 study, a metabolite-profiling and fibroblast-screening exercise. Cardiac repair, angiogenesis, wound healing and the ophthalmic programme belong to thymosin β4; the landmark cardiac paper, Bock-Marquette et al. (Nature, 2004 — frequently miscited as Nature Medicine 2003), studied the parent protein. A listing that quotes it under a TB-500 heading has shown its own conflation before anything is opened.

TB-500 is commonly sold blended with BPC-157, and a blend vial carries no separate identity result for either component unless the certificate reports both masses.

• Mass near 889 Da (TB-500), not near 4,963 Da (thymosin β4), on a batch-matched certificate.
• The CAS on the label: 885340-08-9 is TB-500, 77591-33-4 is thymosin β4. Neither number, or one matching neither compound, means the listing was assembled from other listings.
• The sequence and acetyl cap on the spec sheet: a 43-residue sequence under a TB-500 heading is the parent protein, and an unacetylated seven-mer is not the compound the market means by TB-500 either.
• The research the product page cites: cardiac, angiogenic and ophthalmic results are thymosin β4 results.