Where to Buy SS-31 in 2026: Sizes, Purity Reports and Verification

SS-31 is the research code for elamipretide (INN/USAN), a synthetic tetrapeptide amide with a D-arginine at the N-terminus and 2',6'-dimethyl-L-tyrosine (Dmt) in position 2. Those two residues are the first things a purity report should confirm. This guide covers the chemistry, the sizes Pepta Labs lists, verification, storage and US regulatory status.

What Is SS-31?

The four residues are D-arginine (the D-enantiomer rather than the L-form found in ordinary peptides), Dmt, L-lysine and L-phenylalanine, with a C-terminal primary amide rather than a free acid. Dmt is tyrosine carrying two methyl groups on the aromatic ring, one on each side of the hydroxyl; it is not one of the 20 standard amino acids, and it is why the formula C32H49N9O5 differs from that of Arg-Tyr-Lys-Phe-NH2 by C2H4, or 28.03 Da. A report showing a monoisotopic mass near 611.35 instead of 639.39 is describing the tyrosine peptide, not SS-31. Registry numbers for the whole catalog are collected in the CAS number and molecular weight table.

Salt form and counter-ions

The molecule has three basic sites: the guanidine of arginine, the epsilon-amine of lysine and the free N-terminal amine. All three are protonated in the isolated salt, so up to three acetate (60.05 g/mol each) or trifluoroacetate (114.02 g/mol each) anions accompany each peptide. A fully occupied tri-acetate has a formula weight of about 820 g/mol and a tri-trifluoroacetate about 982 g/mol, against 639.78 g/mol for the free base, so the free base accounts for roughly 78% of the mass of the acetate salt and roughly 65% of the trifluoroacetate salt before bound water is counted. That is why net peptide content is reported separately from purity, and why 25 mg by gross weight is not 25 mg of free base. The salt form and net peptide content are stated on the analytical report; see TFA versus acetate for the arithmetic.

How Pepta Labs Lists SS-31

Both sizes are the same material in a sealed glass vial, listed in the BPC-157 and thymosin category. The product page shows the reported RP-HPLC purity for the sourced production run, and identity is confirmed by mass spectrometry; both results come from an independent laboratory commissioned through a cooperative purchasing group, and Pepta Labs does not test in-house. The analytical report (COA) is available by email on request, before or after purchase. Free US shipping, and most orders ship the next business day. The Testing and Documentation page describes the arrangement.

How to Verify an SS-31 Listing

What the HPLC report shows

Reversed-phase HPLC with UV detection at 214-220 nm separates SS-31 from its synthesis-related impurities, and purity is the main-peak area as a percentage of total peak area. For a tetrapeptide the minor peaks to expect are deletion sequences, the free-acid analogue in which the C-terminal amide has been hydrolysed (about 1 Da heavier), and, if the wrong building block was used, the tyrosine analogue. Area percent does not measure counter-ion, water or fill weight, so a 99.1% purity sits alongside a net peptide content that may be 65-80% without any contradiction.

What the mass spectrometry report shows, and what it cannot

Electrospray MS of a 640 Da peptide gives singly and doubly charged ions that can be compared directly with the monoisotopic mass. An observed [M+H]+ within 0.02 Da of 640.39 on a high-resolution instrument, or within 0.5 Da on a unit-resolution one, is consistent with C32H49N9O5. Two things MS cannot show: it cannot distinguish D-arginine from L-arginine, since enantiomers have the same mass, and it cannot report counter-ion or water content. The stereochemistry rests on the synthesis record and, where available, chiral amino-acid analysis. Peaks 114 Da above the parent are trifluoroacetate adducts from a TFA salt. The expected mass table lists the same figures for the rest of the catalog.

Production-run report versus lot-specific COA

Pepta Labs supplies the report for the sourced production run, the batch from which the vials were filled, tested once by the independent laboratory; it may name the purchasing group or the source as the client rather than Pepta Labs. A manufacturer's lot-specific COA is tied to a numbered lot. Either way, the lot or run reference on the document should match the vial label, the stated formula should be C32H49N9O5, and the observed mass should agree with 639.39 (monoisotopic) rather than 611.35. A certificate with no reference at all should be rejected. The COA verification guide and the HPLC versus mass spectrometry article explain each field.

Storage and Shipping

• Ships as a lyophilized powder at ambient temperature; a few days in transit at room temperature is standard for a sealed, dry peptide.
• Refrigerate at 2-8 C on arrival. For storage longer than a few months, keep the sealed vial at -20 C.
• Protect from light and moisture. Let a cold vial reach room temperature before opening so that condensation does not form on the powder, and keep it sealed between uses.

US Regulatory Status

Elamipretide is the INN and USAN for SS-31. On September 19, 2025 the FDA approved Forzinity (elamipretide hydrochloride), NDA 215244, which appears on the FDA Novel Drug Approvals 2025 page and in Drugs@FDA. The lyophilized SS-31 sold by Pepta Labs is a chemical reference material: it is not Forzinity, is not made under a drug application, and is not a substitute for it. SS-31 does not appear in the FDA section 503A compounding nominations document (updated May 14, 2026) or on the FDA page of bulk substances that may present significant safety risks. The general framework for research compounds is in Peptide Legal Status 2026.

Frequently Asked Questions

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

Yes. Elamipretide is the INN/USAN, SS-31 and MTP-131 are research codes and Bendavia is a former trade designation; all refer to D-Arg-Dmt-Lys-Phe-NH2 (C32H49N9O5, 639.8 g/mol, CAS 736992-21-5).

Why does SS-31 carry several counter-ions per molecule?

Three basic sites (guanidine, epsilon-amine and N-terminal amine) are protonated in the isolated salt, so an acetate or trifluoroacetate salt can hold up to three anions per peptide. This raises the salt formula weight well above 639.8 g/mol and is why net peptide content is reported separately.

Can mass spectrometry confirm the D-arginine?

No. D- and L-arginine have identical masses, so MS confirms the formula but not the stereochemistry. That rests on the synthesis record and, where the report includes it, chiral amino-acid analysis.

All products are supplied for laboratory research use only and are not for human or animal use.