Peptide Molecular Weight Reference Table

Almost everything on a Certificate of Analysis is self-reported. The purity figure, the lab's name, the batch number — you can judge whether they look plausible, but you can't independently confirm them from your desk.

Molecular weight is the exception. A peptide's mass is a fixed property of its chemical structure. If a COA names a peptide and states a theoretical mass, that pairing is either right or wrong, and you can check it in seconds. It's the highest-leverage check available to someone without a chemistry background — which is why a mismatch here is one of the strongest signals that a document was edited from a template.

How to use this table

1. Find the compound your COA names and read off its mass.
2. Compare it to the theoretical mass printed on the COA. These should match closely. A theoretical mass that doesn't correspond to the named compound means the document is internally inconsistent — frequently the fingerprint of a template edited from a different peptide.
3. Compare the observed mass in the mass spectrometry section against that theoretical value, within the tolerance for the instrument used.

Step 2 catches forged paperwork. Step 3 catches the wrong compound in the vial. They fail in different ways, and both are worth doing.

Monoisotopic vs average mass

This distinction causes most false alarms, and most peptide mass lists online ignore it completely.

• Monoisotopic mass uses the lightest, most abundant isotope of each element. It's what high-resolution instruments (ESI, Q-TOF) actually report.
• Average mass uses the natural isotopic average across all elements. It's what most COAs mean when they print a bare "MW" figure.

The gap between the two grows with molecule size — negligible for a tripeptide, but nearly 3 Da for something the size of semaglutide. Compare like with like: checking a high-resolution observed mass against an average theoretical value on a large peptide will "find" a mismatch that isn't there.

Tolerance: how close is close enough?

Real measurements never land exactly on theory. These are workable tolerances by technique:

A difference inside these bounds is ordinary instrument behaviour. A difference of tens or hundreds of daltons is a different molecule.

The reference table

Every entry below is verified against an authoritative source (PubChem or published literature). Masses are in daltons; the table is sorted alphabetically.

* Not a research peptide. MK-677, 5-Amino-1MQ and NAD+ are non-peptide compounds, and glutathione is a tripeptide rarely handled as one; all four are listed because they appear in the same catalogs and on the same COAs.

For the two largest entries — IGF-1 LR3 and HGH (191aa) — only average mass is given. At that size monoisotopic mass isn't a practical comparison: the isotope envelope is broad enough that instruments report an average, and that's what a COA will quote.

Where the "right" mass is genuinely ambiguous

A few widely sold names don't map to a single molecule. If a COA's mass doesn't match the headline figure, check whether the compound is one of these before concluding anything is wrong.

TB-500

In the research market the name is used for full-length Thymosin Beta-4 (43 amino acids, ~4,963 Da average), and that's the practical default. But the literal TB-500 fragment — Ac-LKKTETQ — is a far smaller molecule at ~889 Da. Both are defensible readings of the label; they're simply different compounds.

GHK-Cu and AHK-Cu

Copper peptides may be reported as the copper complex or as the bare tripeptide. GHK-Cu appears at ~400.9 Da as the complex and ~340.4 Da bare; AHK-Cu at ~418.0 Da as the complex and ~354.4 Da bare. A COA reporting the bare peptide mass isn't wrong — it's describing a different form of the product.

CJC-1295 with and without DAC

These are separate rows in the table for a reason: with DAC it's ~3,647 Da average, without it ~3,368 Da. A vendor listing plain "CJC-1295" is omitting information you need before the mass can be checked at all.

Blends have no molecular weight

Some products are mixtures, not compounds. A mixture has no single molecular weight, so a COA claiming one is describing something that cannot exist:

• Lipo-C — Lipotropic blend (e.g. methionine/inositol/choline + B-vitamins).
• GLOW — Blend (commonly GHK-Cu + BPC-157 + TB-500).
• KLOW — Blend (commonly GHK-Cu + KPV + BPC-157 + TB-500).
• Thymalin — Polypeptide extract/complex from thymus.

For a blend, a meaningful COA reports each component separately. A single mass figure for a multi-component product is a red flag on its own.

Why salt form doesn't change these numbers

A common source of confusion: peptides ship as TFA or acetate salts, and those counterions add real weight to the powder in the vial. They do not change the peptide's molecular weight. The masses here are for the peptide itself — which is what mass spectrometry measures and what a COA's theoretical mass refers to.

Counterion weight affects a different number entirely: net peptide content, the fraction of the powder that is actually peptide. If your question is how much peptide is in the vial rather than whether it's the right peptide, see purity vs net peptide content.

What a real mismatch means

If the mass is off by far more than tolerance, there are only a few explanations:

• The document was edited from another peptide's template — the most common cause, usually accompanied by other forgery markers.
• The vial contains a different compound than the label claims.
• The wrong form was reported — one of the variant cases above, worth ruling out first.
• Monoisotopic/average confusion, which looks like a discrepancy of a few daltons on a large peptide, not a large one.

Rule out the last two before assuming the first two. But a mass wrong by hundreds of daltons has no innocent explanation.

Frequently asked questions

Research use only. This article is for scientific and educational purposes and is not medical, dosing, or investment advice. Research peptides are not approved for human or veterinary use. Masses are provided for documentation-checking purposes; verify against an authoritative source before relying on them for analytical work.