TB-500 testing: what a full panel shows and how TB-500 samples fail in published tests

What a TB-500 test should show

A TB-500 test should answer three questions in this order: which molecule is in the vial, how pure it is, and how many mg of it the vial holds. The first question matters more for TB-500 than for most peptides, because sellers use the name for more than one molecule. A purity figure means little until the lab has shown, by mass, that the main peak is the molecule on the label.

Test	What it answers for TB-500	Unit
Identity (LC-MS)	Is the main peptide full-length thymosin β4, a fragment, or something else?	Observed vs expected mass
Purity (HPLC)	What share of the UV-absorbing material is the target peptide?	% peak area
Content per vial	How many mg of the target peptide, against a reference standard of the same molecule	mg per vial, % of label
Endotoxin (LAL)	How much bacterial endotoxin is in the vial	EU per mg and per vial
Sterility (USP <71>, 14 days)	Did microbes grow from the tested units in 14 days?	Growth or no growth

Purity and content are two different numbers. A vial can be 99.6% pure and still hold half the mg on the label. Our guide to net peptide content explains why the powder weight and the peptide weight differ.

Which molecule is “TB-500”?

Lab menus show the problem. Janoshik lists one test for “TB4/TB-500/TB4(17-23)”. Chromate lists TB-500 (43 aa) and TB-500 (17-23) as two separate tests. The two molecules are far apart:

• Full-length thymosin β4: 43 amino acids, N-terminally acetylated, average mass about 4,963 Da (calculated from the formula C212H350N56O78S).
• The 17–23 fragment: 7 amino acids, under 1,000 Da.

Mass spectrometry tells them apart easily. Retention time alone does not prove which one is present, which is why identity needs LC-MS. The real risk is a mismatch of expectations. If the label says “TB-500” and the lab looks only for the fragment, a vial of full thymosin β4 could be reported as a failure, or the reverse. A useful report prints the exact sequence the lab tested for.

How TB-500 samples fail in published tests

Finnrick publishes pass and fail counts per product. Its public data summary of 25 September 2026 lists 282 TB-500 tests from 58 vendors: 103 passed and 175 failed under its default “Purity Focus” standard (HPLC purity of at least 99.5% and fill within ±35% of the label). The first published TB-500 test is dated 16 May 2025.

Finnrick’s TB-500 page shows the 200 most recent tests (29 January to 25 September 2026), and each test page prints the reason for a fail. We counted those reasons on 4 October 2026:

Result	Tests
Pass	83
Fail: purity below 99.5% only	76
Fail: not the labelled substance	26
Fail: purity and fill both out	7
Fail: fill outside ±35% only	4
Incomplete	4

Three details stand out:

• Most purity failures were near misses. Of 83 purity failures, 52 read between 98.0% and 99.4%. Only 5 read below 90%. Under a 98% purity bar, most of these vials would clear purity.
• Identity failures cluster on the plain name. Of the 26 vials that were not the labelled substance, 23 were sold as plain “TB-500” with no variant recorded. Three were sold as thymosin β4 and none as the 17–23 fragment. Plain “TB-500” listings were about 60% of the 200 tests but 23 of the 26 identity failures. The data do not say why, but it fits the naming problem above.
• Fill failures ran both ways. Six vials were under the label by more than 35% and five were over.

Thresholds differ. Finnrick’s default purity bar is 99.5%, while Vanguard logs a purity fail below 98.9%, according to Krysia’s analysis of its failed-samples log. Compare a result with the rule it was judged against, not with a bare “pass” or “fail”. Our guide to which peptides fail most often compares TB-500 with other compounds.

Pitfalls specific to TB-500

• No sequence on the report. If a report says only “TB-500”, you cannot tell which molecule passed.
• No matching reference standard. Content per vial needs a standard of the same molecule. A fragment standard cannot quantify full thymosin β4.
• Blends. TB-500 is often sold with BPC-157, and in larger mixes. A blend needs identity and mg for each component; one purity number for the whole vial means little. See testing peptide blends.
• Salt form. Content should be stated as free base. Acetate or TFA salt adds weight that is not peptide.

How to read a TB-500 test result

1. Find the molecule the lab tested for. It should be a sequence or a formula, with your label claim marked as client-supplied.
2. Check identity by mass: expected mass, observed mass and the error.
3. Read purity as a share of UV peak area, at a stated wavelength, with the chromatogram attached.
4. Read content in mg with its basis (free base or salt), the reference standard and the uncertainty, then compare it with the label.
5. Check the batch on the report against the batch on your vial, and verify the report on the lab’s own site.

How to send a TB-500 sample

Send the vial unopened and freeze-dried, in its original state, with its batch number visible. Sterility needs its own unopened vials, so ask how many vials each test needs before you post. If you want to know how much vials in one batch differ, send several vials from the same batch. Our guide on how to send peptides for testing covers packing and labels.

What HK Analytical runs for TB-500

Our TB-500 compound page lists the panel for a freeze-dried vial: identity by LC-MS, purity by HPLC, content per vial, endotoxin (LAL) and Sterility (USP <71>, 14 days). The report prints the exact sequence we tested for and marks your claim as client-supplied. Every number comes with its raw data, the report is a signed record you can check on hkanalytical.com/verify, and it carries our own photo of the vial as received. Results within days of receipt. Sterility (USP <71>, 14 days) is the one test that takes 14 days, because the method incubates for 14 days. We do not offer blend analysis per component. See the example report or ask for a quote.