Two chains of very different length
BPC-157 is a synthetic peptide of fifteen residues. Its sequence in single-letter notation is GEPPPGKPADDAGLV, its N-terminus is a free amine, and its C-terminus is a free acid. Everything about how it behaves on an instrument follows from that short, proline-rich chain, which is described residue by residue in BPC-157: peptide identity, purity, and stability.
"TB-500" is a less precise name. It is used by different suppliers for two different molecules: the full 43-residue thymosin beta-4 sequence, and a short fragment built around seven of its residues. The TB-500 5mg listing on this site publishes CAS 77591-33-4, the formula C212H350N56O78S, and a molecular weight of 4,963.4 g/mol, which is the full 43-residue chain SDKPDMAEIEKFDKSKLKKTETQEKNPLPSKETIEQEKQAGES carrying an acetyl group on its N-terminus. That is the material this page compares. The naming problem itself, and the roughly 900 g/mol fragment, are covered in TB-500 and thymosin beta-4: what the name covers.
| Property | BPC-157 | TB-500 (thymosin beta-4) |
|---|---|---|
| Residue count | 15 | 43 |
| N-terminus | Free amine | Acetylated |
| Molecular formula | C62H98N16O22 | C212H350N56O78S |
| Theoretical monoisotopic mass | approximately 1,418.7 | approximately 4,960.5 |
| Theoretical average mass | 1,419.5 g/mol | 4,963.4 g/mol |
| CAS registry number | 137525-51-0 | 77591-33-4 |
| Sulfur in the formula | None | One (a single methionine) |
| Acidic vs. basic residues | 3 acidic (Glu, Asp, Asp) vs. 1 basic (Lys) | 11 acidic (8 Glu, 3 Asp) vs. 9 basic (Lys) |
| Physical form supplied | Lyophilized solid | Lyophilized solid |
The masses above are calculated from the formulas on the listings; treat them as orientation. The report for a specific lot is the authoritative record, and where it disagrees with this page, the report governs.
Composition, and what it predicts on a chromatogram
Reading the two sequences tells you what the impurity peaks on each chromatogram are likely to be before you see either trace.
- BPC-157 has four prolines, three of them consecutive, and two adjacent aspartates. Proline couples inefficiently, so deletion sequences — the chain missing one residue — are the expected synthesis impurity, and they elute close to the main peak because a 14-residue chain is chemically very similar to the 15-residue one. The aspartate pair can rearrange into a species of identical mass, which is why the chromatogram and the identity result have to be read together. With no methionine and no cysteine, oxidation is not its characteristic failure.
- Thymosin beta-4 has 42 couplings, nine lysines, and one methionine. Nearly three times as many coupling steps means nearly three times as many places for a deletion to occur, so a full-length lot tends to carry a broader family of near-eluting deletion sequences than a short peptide does, and its purity figure should be read with that in mind. The single methionine oxidises readily; the oxidised species is 16 mass units heavier than the parent and is resolvable by mass spectrometry directly. The N-terminal acetyl group is a third point: an unacetylated chain (C210H348N56O77S) sits about 42 units lower, near 4,921 g/mol average, so the mass on a report also tells you which form the reference standard describes.
- They do not share a reference standard. The two peptides elute at different retention times under any single method, so a retention-time identity result — reported as HPLC-RTM on a certificate — is only meaningful when the report names which reference standard the retention time was matched against. A standard for one material says nothing about the other.
For how these peaks are integrated and reported, see how to read an HPLC chromatogram.
Theoretical mass, and how each appears in a mass spectrum
The largest difference between the two reports is in the mass-spectrometry section, and it is a difference of kind rather than degree.
A 1,419 g/mol peptide with a single lysine and a free N-terminus picks up one or two protons when ionised. On a BPC-157 report the observed ions are therefore the singly charged species near m/z 1,419.7 and the doubly charged species near m/z 710.4, and the observed mass can be read almost directly off the spectrum.
A 4,960 g/mol peptide with nine lysines behaves differently. It is rarely seen as a singly charged ion at all. Instead it appears as an envelope of multiply charged ions — for the acetylated form, near m/z 1,654.5 (three protons), 1,241.1 (four), and 993.1 (five) — and the instrument software deconvolutes that envelope back to a single neutral mass. The report should state that deconvoluted mass, near 4,960 to 4,963 depending on whether the laboratory reports monoisotopic or average values, and it should state which.
The practical consequence is worth stating plainly. A raw m/z value in the 700 to 1,700 range can legitimately appear on either report. A line that reads "observed m/z 1,241" with no charge state and no deconvoluted mass has not identified either material; it is a number without the information needed to interpret it. HPLC purity versus mass-spectrometry identity covers what each result does and does not establish.
What each certificate of analysis must show
| Report section | For a BPC-157 lot | For a TB-500 (thymosin beta-4) lot |
|---|---|---|
| Identity | Observed mass in agreement with 1,419.5 g/mol within the method's tolerance, or HPLC-RTM against a named BPC-157 reference standard | Deconvoluted mass in agreement with 4,963.4 g/mol (acetylated) within tolerance, with the charge states listed, or HPLC-RTM against a named thymosin beta-4 reference standard of stated form |
| Chromatographic purity | Main-peak area as a percentage of total integrated area, with the chromatogram published; near-eluting deletion peaks are the expected signature | The same figure and trace; expect a broader set of near-eluting deletion peaks, and look for a resolved +16 oxidation peak if one is present |
| Method fields | Column, mobile phase or gradient, detection wavelength, and reporting limit. A percentage with no method attached is not a result. | |
| Record fields | Material name, labeled strength, lot identifier matching the vial label, test date, certificate number, and the issuing laboratory with its verification route. | |
Neither report is complete with only one of the two results. A mass agreement without a chromatogram says nothing about what else is in the vial; a purity percentage without an identity result says nothing about what the main peak is. The certificate of analysis glossary defines each field above the way a receiving laboratory uses it.
How to tell them apart on paper
If a report has been attached to the wrong listing, or a listing's name and its document disagree, five checks settle it without an instrument.
- Find the stated theoretical mass. Near 1,419 is BPC-157. Near 4,963 is the full thymosin beta-4. Near 900 is the short fragment sold under the TB-500 name. There is no overlap between the three.
- Count the residues if a sequence is printed. Fifteen against forty-three; a count anywhere in between describes a deletion product, not either parent.
- Look for sulfur in the formula. BPC-157's formula contains no S. Thymosin beta-4's contains exactly one, from its methionine.
- Read the mass-spectrometry section for charge states. One or two charge states with a top ion near 1,420 is the small peptide; an envelope of three or more charge states resolving to a mass near 4,960 is the large one.
- Check that the identity line names a reference. An HPLC-RTM result has to say which material the retention time was matched against; if it does not, it has not distinguished anything.
Common documentation gaps
The gaps below recur across listings for both materials, and each one is visible from the document alone.
- A generic datasheet in place of a lot report. A page of "typical values" with no lot identifier describes what the material is supposed to be, not what a laboratory measured in the batch being sold.
- One PDF across strengths or products. The same certificate number attached to a 5mg listing, a 10mg listing, and a "BPC-157 + TB-500" blend page means at most one of those was analysed. A blend has its own reporting requirements, covered in what a blend COA has to show.
- A mass with no charge state or no stated form. For thymosin beta-4 in particular, an m/z value without its charge, or a mass without stating whether the acetylated chain is meant, leaves the identity result uninterpretable.
- "TB-500" with no mass and no reference named. The report has not said which of the two molecules the vial contains.
- A purity percentage without the chromatogram. The figure cannot be checked, and for a proline-rich or long chain the near-eluting peaks are the informative part.
- No CAS number and no laboratory named. Without a CAS number the identity result has no reference to be compared against; without a named laboratory the document rests on the seller's word. How to verify a certificate covers the verification step.
Which lots are documented on this site
The state of the record as of this page's date, stated plainly so it can be checked against the pages it describes.
- BPC-157 5mg — lot BCP-2502-B: 99.59% (HPLC), tested Aug 25, 2026, certificate COA-2026-Q53ZYU, issued by ILS Labs, with the original PDF and the laboratory's verification link on the lot page. The earlier lot BCP-2501-A (99.566%, Feb 27, 2026, Janoshik) remains published on the listing as a historical record.
- BPC-157 10mg — no exact-lot report is currently published for this strength. The listing shows the 5mg record as a product-family reference and labels it as such.
- TB-500 5mg — the listing publishes the CAS number, formula, and molecular weight given above. No lot-specific report is currently published for this material on this site, which is the same statement any listing should be able to make about itself when it is true.
The BPC-157 materials page collects both strengths and their documentation status in one place, and the best BPC-157 supplier checklist sets out six checks that apply to any listing of this compound, including these.