Peptide reference · Synthetic tetrapeptide (contains non-standard residues)

SS-31 (Elamipretide) COA check: molecular weight, formula and what to look for

By the PeptideCOACheck team · Last updated November 2, 2026 · How we check

Use these reference values to check the identity result on a SS-31 (Elamipretide) Certificate of Analysis. The theoretical average molecular weight of SS-31 (Elamipretide) is 639.79 Da and the monoisotopic mass is 639.386 Da.

Check a SS-31 (Elamipretide) COA now

FP · 639.3857 Fingerprint calculated from the formula: positions of the protonated ions, the natural isotope pattern of the neutral molecule (relative heights are calculated; ion heights are schematic) and the atom mix. It is a reference picture, not measured data.

SS-31 (Elamipretide) reference data

Name	SS-31 (Elamipretide)
Also known as	Elamipretide, MTP-131, Bendavia
Type	Synthetic tetrapeptide (contains non-standard residues)
Molecular formula	C₃₂H₄₉N₉O₅
Average molecular weight	639.79 g/mol (Da)
Monoisotopic mass	639.3857 Da
Residues	4
Sequence	D-Arg-Dmt-Lys-Phe-NH₂
Reference source	PubChem CID 11764719 (formula and mass cross-checked)

Expected mass spectrometry ions

A SS-31 (Elamipretide) COA may list one of these m/z values instead of the neutral mass. That is still consistent with SS-31 (Elamipretide). How charge states work.

Ion	m/z (monoisotopic)	m/z (average)
[M+H]⁺	640.39	640.80
[M+2H]²⁺	320.70	320.90
[M+3H]³⁺	214.14	214.27

What else can show up on a SS-31 (Elamipretide) COA

Masses calculated from SS-31 (Elamipretide)'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)	661.37 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)	677.34 Da	Potassium adduct: an MS artifact. The [M+K]+ ion itself is at M + 38.96
TFA adduct (M + 113.99)	753.38 Da	Trifluoroacetic acid from purification seen as an adduct; residual TFA salt is real vial content
M + 0.98 (free acid)	640.37 Da	C-terminal amide hydrolysed or free-acid synthesis error

Deletion sequences (4): one residue missing

Signal	Value	What it means
des-Arg (M − 156.10)	483.28 Da	Deletion sequence missing one Arg
des-Dmt (M − 191.09)	448.29 Da	Deletion sequence missing one Dmt
des-Lys (M − 128.09)	511.29 Da	Deletion sequence missing one Lys
des-Phe (M − 147.07)	492.32 Da	Deletion sequence missing one Phe

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 SS-31 (Elamipretide) (4 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.

SS-31 (Elamipretide)-specific things to watch

SS-31 (elamipretide) is a four-residue amidated peptide containing 2',6'-dimethyltyrosine (Dmt), about 639.8 Da.

It is highly basic (three positive charges at neutral pH), so ESI spectra often show strong [M+2H]²⁺ (about 320.7 m/z) and [M+3H]³⁺ (about 214.1 m/z) ions in addition to [M+H]⁺.

It is commonly supplied as an acetate or trifluoroacetate salt, which affects net peptide content but not the measured peptide mass.

Elamipretide is also known as SS-31 and MTP-131. Because it carries several positive charges, its [M+H]+ at 640.39 m/z is often weaker than the 2+ ion at 320.7 m/z.

Watch a low-resolution report: the free-acid impurity has a neutral mass of 640.37 Da, almost exactly the [M+H]+ value of the real product (640.39 m/z). A COA that just says "640" doesn't make clear which it measured, so ask whether the figure is a neutral mass or an m/z reading.

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.

NAD+: 663.43 Da (+23.64 Da)
Ipamorelin: 711.85 Da (+72.06 Da)
Selank: 751.87 Da (+112.08 Da)

Sources

PubChem CID 11764719: SS-31 (Elamipretide) 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.

Last updated November 2, 2026. Written and maintained under our editorial policy. Found an error? See corrections.

Frequently asked questions

Are SS-31, MTP-131 and elamipretide the same?

Yes. They're names for the same tetrapeptide, D-Arg-Dmt-Lys-Phe-NH2, about 639.8 Da.

What does 320.7 m/z mean on an elamipretide COA?

The [M+2H]2+ ion. Elamipretide's positive charges make the 2+ ion strong.

Does the TFA salt change elamipretide's measured mass?

No. The counter-ion separates in the instrument. It lowers net peptide content per milligram, not the peptide 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.