Peptide reference · Synthetic heptapeptide (ACTH 4-7 analog)
Semax COA check: molecular weight, formula and what to look for
Use these reference values to check the identity result on a Semax Certificate of Analysis. The theoretical average molecular weight of Semax is 813.92 Da and the monoisotopic mass is 813.348 Da.
Check a Semax COA nowSemax reference data
| Name | Semax |
|---|---|
| Also known as | ACTH(4-7)-PGP |
| Type | Synthetic heptapeptide (ACTH 4-7 analog) |
| Molecular formula | C37H51N9O10S |
| Average molecular weight | 813.92 g/mol (Da) |
| Monoisotopic mass | 813.3480 Da |
| Residues | 7 |
| Sequence | Met-Glu-His-Phe-Pro-Gly-Pro |
| Reference source | PubChem CID 9811102 (formula and mass cross-checked) |
Expected mass spectrometry ions
A Semax COA may list one of these m/z values instead of the neutral mass. That is still consistent with Semax. How charge states work.
| Ion | m/z (monoisotopic) | m/z (average) |
|---|---|---|
| [M+H]+ | 814.36 | 814.93 |
| [M+2H]2+ | 407.68 | 407.97 |
| [M+3H]3+ | 272.12 | 272.31 |
What else can show up on a Semax COA
Masses calculated from Semax's formula and sequence for the adducts, degradation products and synthesis impurities a lab report can show. A match tells you what the extra peak probably is.
| Signal | Value | What it means |
|---|---|---|
| Na adduct, deconvoluted (M + 21.98) | 835.33 Da | Sodium adduct: an MS artifact, not a separate impurity. The [M+Na]+ ion itself is at M + 22.99 |
| K adduct, deconvoluted (M + 37.96) | 851.30 Da | Potassium adduct: an MS artifact. The [M+K]+ ion itself is at M + 38.96 |
| TFA adduct (M + 113.99) | 927.34 Da | Trifluoroacetic acid from purification seen as an adduct; residual TFA salt is real vial content |
| M + 16 (oxidation) | 829.34 Da | Oxidation of Met |
Deletion sequences (6): one residue missing
| Signal | Value | What it means |
|---|---|---|
| des-Met (M − 131.04) | 682.31 Da | Deletion sequence missing one Met |
| des-Glu (M − 129.04) | 684.31 Da | Deletion sequence missing one Glu |
| des-His (M − 137.06) | 676.29 Da | Deletion sequence missing one His |
| des-Phe (M − 147.07) | 666.28 Da | Deletion sequence missing one Phe |
| des-Pro (M − 97.05) | 716.30 Da | Deletion sequence missing one Pro |
| des-Gly (M − 57.02) | 756.33 Da | Deletion sequence missing one Gly |
Adduct rows are deconvoluted masses (the shift seen against [M+H]+); the singly charged [M+Na]+ ion itself sits at M + 22.99. Deletion masses alone can't say which copy of a repeated residue is missing.
Short peptides like Semax (7 residues) are easy to make cleanly, so 98% HPLC purity should be the floor, not the goal. The full checklist is in how to read a peptide COA.
Semax-specific things to watch
Semax is the ACTH 4-7 fragment (MEHF) extended with Pro-Gly-Pro, about 813.9 Da.
It begins with methionine, which is prone to oxidation. A main peak about 16 Da above the expected mass suggests oxidized material; this checker flags that pattern.
N-Acetyl Semax Amidate is a different product (acetylated and amidated) with a different mass. Make sure the product name on the COA matches exactly.
Semax starts with methionine, so oxidation (+16 Da, [M+H]+ near 830.4 m/z) is the first thing to look for. Liquid products such as nasal sprays oxidize faster than dry powder, so the test date relative to the bottling date matters.
N-Acetyl Semax Amidate is a different product: acetylated and amidated, about 854.4 Da monoisotopic (855.0 average). A COA for plain Semax that reads near 854 or 855 is the wrong compound.
Regulatory note, as of November 2, 2026. On October 28, 2026, HHS issued an interim enforcement discretion policy for 503A pharmacy compounding of six peptides: BPC-157, Epitalon, KPV, MOTS-c, Semax and TB-500. It covers single-ingredient preparations made by state-licensed pharmacies and physicians under listed conditions; blends are not covered, and it does not approve these peptides as drugs. For reading a COA, the useful detail is that the policy names specific forms (here, Semax free base (intranasal)), so a COA that states the salt form tells you more than one that does not.
Compounds with similar mass
If a COA's mass is off, compare it with these neighbors. A match to one of them can point to a mislabeled product.
Sources
- PubChem CID 9811102: Semax formula and reference mass.
- CIAAW: Standard atomic weights: Used to calculate average molecular weights.
- NIST CODATA: proton mass: Used to convert m/z charge states to neutral mass.
- PeptideCOACheck methodology: How the checker's thresholds work.
- HHS will permit compounding of six peptides ahead of formal rulemaking (RAPS, Oct 29, 2026): Summary of the October 28, 2026 HHS enforcement discretion policy.
- Federal Register public inspection, FR Doc 2026-22192: The policy document itself.
Last updated . Written and maintained under our editorial policy. Found an error? See corrections.
Frequently asked questions
What mass should N-Acetyl Semax Amidate show?
About 854.4 Da monoisotopic or 855.0 average, roughly 41 Da above plain Semax.
What does a peak near 830 m/z mean on a Semax COA?
[M+H]+ of oxidized Semax: one methionine has picked up an oxygen.
Does Semax free base vs acetate change the COA mass?
No. It changes net peptide content per milligram, not the peptide's measured mass.
For laboratory research use only. This page describes analytical chemistry data. It is not medical advice and makes no claim about effects in humans or animals.