An SS-31 certificate of analysis is a lot-specific test record, not a quality guarantee. Read six fields closely: identity method, purity method with its chromatogram, net peptide content and salt form, lot number matching the vial, test date, and the laboratory that signed it. Verify each at the bench.
- A certificate of analysis applies only to the lot printed on it, and a lot number that does not match the vial makes the document irrelevant.
- SS-31 is the tetrapeptide D-Arg-2',6'-dimethyl-Tyr-Lys-Phe-NH2, formula C32H49N9O5, free base molecular weight near 639.8, later named elamipretide.
- HPLC area percent excludes counterion, water and anything without a chromophore at the detection wavelength, so it is not a mass purity figure.
- Mass spectrometry cannot distinguish D-arginine from L-arginine, so stereochemistry stays unestablished without a chiral method or reference standard.
- With three basic sites on the molecule, salt counterion plus residual water can account for a substantial fraction of the labelled fill weight.
- Verification that means anything happens at the issuing laboratory or on your own instruments, not in correspondence with the seller.
What the document claims, and what it does not
A certificate of analysis is a record of tests performed on one specific lot of material at one specific time. That is the whole of its authority. It does not certify the vial in your hand unless the lot identifier on the vial matches the lot identifier on the certificate, and it says nothing about how the material was handled between the test date and your bench.
For SS-31 this matters more than for a simple small molecule. The compound is a tetrapeptide, D-Arg-2',6'-dimethyl-Tyr-Lys-Phe-NH2, described in the Szeto-Schiller series of aromatic-cationic mitochondria-targeting peptides and later given the international nonproprietary name elamipretide. The free base has formula C32H49N9O5 and a molecular weight near 639.8. Three basic sites sit on that short backbone: the guanidine of arginine, the ε-amine of lysine and the N-terminal amine. Short, highly basic peptides are shipped as salts, and salt form is where a great many net-content errors originate.
So the certificate has two jobs. It should establish that the material is the intended molecule, and it should quantify how much of that molecule is present per vial. Most circulating documents do the first job adequately and the second job badly or not at all.
- Identity — method named, observed mass and charge state given
- Purity — area percent with column, gradient, wavelength and the trace
- Net content — peptide content, not just nominal fill
- Counterion and water — quantified, not omitted
- Lot number — character-for-character match with the vial
- Test date and issuing laboratory — a date of analysis and a named entity
Field by field
| Field | What it should say | How it fails |
|---|---|---|
| Product name and synonyms | SS-31, with elamipretide named; sequence written out in three-letter code showing D-Arg and Dmt | Trade or code names only, no sequence, no stereochemistry indicated |
| CAS number | A registry number, with free base and salt distinguished; 736992-21-5 is commonly cited for elamipretide free base and should be checked against the registry rather than trusted from a vendor page | One number given for a salt lot, or a number that belongs to an unrelated peptide |
| Molecular formula and mass | C32H49N9O5, 639.8 free base, with the salt form stated separately | Salt mass quoted as if it were the free base, or no formula at all |
| Appearance | White to off-white lyophilized powder or cake | Copied text that contradicts what is in the vial |
| Identity | Method named: ESI-MS or HRMS, with the observed ion and charge state | "Conforms" with no method and no observed mass |
| Purity | RP-HPLC area percent at a stated wavelength, with column, gradient and run time, plus the chromatogram | A bare percentage, usually 99% or higher, with no trace attached |
| Net content | Nominal fill and, separately, peptide content determined by amino acid analysis or nitrogen determination | Nominal fill only, presented as if it were peptide mass |
| Counterion and water | Acetate or trifluoroacetate quantified; water by Karl Fischer or thermogravimetry | Absent entirely, which is the single most common gap |
| Lot number | Matches the vial label character for character | Blank, handwritten, or a batch code that appears on every certificate the supplier sends |
| Test date and issuer | Date of analysis, laboratory name, address, analyst or authorised signatory | Issue date only; a logo with no legal entity behind it |
Print the certificate and read it against the vial before the vial is opened. Discrepancies found afterwards are much harder to act on.
Identity: mass is necessary and not sufficient
Electrospray mass spectrometry on a 639.8 free base gives a singly protonated ion near m/z 640.8 and, because the molecule carries multiple basic sites, a doubly charged species near m/z 320.9 is routinely the more intense signal. A certificate that reports one of these, states the charge state and names the instrument mode has done real work. A certificate that says only "MS: conforms" has told you that somebody looked.
Mass resolves some substitution errors well. The 2',6'-dimethyltyrosine residue is not a coded amino acid, and a lot in which mono-methyltyrosine or plain tyrosine was carried through the synthesis differs by 14 or 28 mass units. That is trivially visible. Deletion of any residue is visible. Incomplete side-chain deprotection is visible.
Mass resolves stereochemistry not at all. The arginine at position one is the D enantiomer, and the D and L forms are isobaric. An SS-31 lot synthesised with L-Arg by error, or one carrying partial racemisation from a slow coupling step, will pass a mass check without a murmur. Distinguishing them needs a chiral method, or co-injection against a qualified reference standard on a chromatographic system where the epimer is known to separate. Very few research-grade certificates address this. If the work depends on the stereochemistry being right, the honest position is that a mass spectrum alone leaves it unestablished.
Purity: what an area percentage covers
Purity on a peptide certificate almost always means reversed-phase HPLC area percent: the peak of interest as a fraction of total integrated peak area, usually with UV detection at 214 or 220 nm where the amide backbone absorbs. USP General Chapter <621> sets the framework for how such a chromatographic procedure is described and how system suitability is demonstrated, and a certificate that reports a number without the column, mobile phases, gradient and detection wavelength cannot be reproduced by anyone.
Three things an area percentage does not include. It does not include anything that fails to elute in the run window, so a short gradient can hide late-eluting hydrophobic material. It does not include anything without a chromophore at the detection wavelength, which is why counterion and residual salts sit outside the number entirely. And it is an area fraction, not a mass fraction: response factors differ between the main peak and its related substances, so 98.5% area is an approximation of 98.5% by mass, not a synonym for it.
Ask for the chromatogram. A trace shows the baseline, the peak shape, whether integration was cut generously and whether there is a shoulder that the reported number quietly absorbed. ICH Q3A(R2) formalised, for drug substances, the practice of setting thresholds at which an impurity must be reported, identified and qualified. Research material is outside that framework, but the logic transfers: a 1.5% unidentified peak is a question, not a rounding error.
Net content, counterion and the arithmetic that follows
This is where documentation for basic peptides most often misleads, and it is not usually deliberate. A vial labelled 50 mg has 50 mg of powder in it. The powder is a salt, and it holds water. Peptide content is the fraction that is actually SS-31.
| Component | Typical range | How it is measured |
|---|---|---|
| Trifluoroacetate, if TFA salt | Up to roughly a third of gross mass at full stoichiometry; commonly 10–20% in practice | Ion chromatography or 19F NMR |
| Acetate, if acetate salt | Lower per mole than TFA; commonly 5–12% | Ion chromatography or titration |
| Water | 2–8% in a lyophilizate | Karl Fischer titration or thermogravimetry |
| Residual solvent | Trace | Headspace GC |
| Peptide | The remainder | Amino acid analysis or nitrogen determination |
Work an example. A nominal 50 mg fill, TFA salt, with measured TFA at 18% and water at 5%, gives a peptide content near 77%:
50 mg × 0.77 = 38.5 mg peptide
Bring that vial into 2 mL of diluent and the actual concentration is:
38.5 mg ÷ 2 mL = 19.3 mg/mL
Against an assumed 25 mg/mL, that is a 23% low bias carried into every downstream calculation, invisibly. The vial concentration calculator handles the arithmetic once you have the peptide content figure; what it cannot do is invent the figure when the certificate omits it. The same correction belongs in any price comparison, since cost per mg of gross powder and cost per mg of peptide diverge by exactly this margin. Diluent choice is a separate record entry; see the note on bacteriostatic water for what belongs in it.
Lot match, test date and the issuing laboratory
Three fields do the traceability work, and all three are routinely treated as decoration.
Lot match is binary. If the string on the vial and the string on the certificate differ in any character, the certificate describes different material and should be treated as absent. A supplier sending one certificate to cover several shipments over months is telling you, unintentionally, that lot control is not being maintained.
Test date is not issue date. Peptides are tested at release and then stored, sometimes for a long time. A certificate dated eighteen months before shipment is still a valid record of what the material was at release; it is not evidence of what arrived. Storage conditions during that interval belong in the supplier's documentation, and if the interval is long, a purity re-check on receipt is the reasonable response.
The issuing laboratory should be a named legal entity with an address and a signatory. In-house quality control at the manufacturer is normal and acceptable, as long as it is identified as such. What is not acceptable is a document with a graphic and no entity, or a third-party laboratory named without a report number that the laboratory itself could confirm. Our own quality standard page sets out which of these documents we hold per lot and which we do not claim to.
Verifying at the laboratory rather than with the seller
Asking a supplier whether their certificate is genuine has an obvious flaw. Verification that means anything happens either at the issuing laboratory or on your own instruments.
Where a third-party laboratory is named, contact that laboratory with the report number and ask them to confirm the document exists and matches what they issued. Reputable analytical services expect this request. A refusal, or a report number the laboratory does not recognise, ends the conversation about that supplier.
On your own bench, three checks cover most of the ground. Run the lot on your RP-HPLC method and compare retention time and peak profile against a qualified reference standard, if you have one, or against a previous lot from the same source; a shift in retention time on an unchanged method is a flag before any purity number is calculated. Confirm the mass by LC-MS, recording the charge state you observed rather than the one you expected. And weigh the vial contents where the protocol allows destructive check, since gross fill weight is the one claim you can test without any instrument at all.
Keep the certificate in the lot record, not in an inbox. When a result later looks wrong, the first question is whether the material was what the protocol assumed, and a record that ties the sample through the aliquot to the vial to the certificate answers it quickly.
Red flags in circulating certificates
- Purity stated as 99% or higher on every lot, every time, with no chromatogram. Real synthesis varies.
- Identity reported as "conforms" with no observed mass and no method named.
- No counterion line and no water content, on a peptide with three basic sites.
- Molecular weight quoted as 639.8 for a lot explicitly described as a salt.
- Sequence written without stereodescriptors, so D-Arg is not distinguished from L-Arg.
- Lot field blank, handwritten, or identical across unrelated orders.
- Issue date present, analysis date absent.
- Therapeutic language anywhere on the document. A certificate that describes what the compound does for a condition is a marketing sheet wearing a lab coat, and its numbers deserve the same scepticism.
None of these individually proves the material is wrong. Each one narrows what the document can support.
Regulatory position
SS-31 is the Szeto-Schiller designation for the tetrapeptide later named elamipretide, also seen as MTP-131. It has been through late-stage clinical investigation, including programmes in Barth syndrome and primary mitochondrial myopathy, and its regulatory position moved during 2025. Anyone who needs the current status should read it from the FDA's own records rather than from a supplier page or a secondary summary, including this one.
What does not change with regulatory status: material supplied as a research chemical is not manufactured under pharmaceutical quality systems, carries no sterility or endotoxin release, and has never been a lawful route to human use at any point. A certificate of analysis covering identity and purity is a narrower claim about a different kind of material than a drug product specification.
Status of this note verified 26 August 2026; confirm current FDA status directly.
FOR LABORATORY AND IN-VITRO RESEARCH USE ONLY. NOT FOR HUMAN OR ANIMAL CONSUMPTION. NOT FOR PERSONAL, MEDICAL, DIAGNOSTIC, THERAPEUTIC, OR RECREATIONAL USE.
What is SS-31 studied for?
Published research on SS-31 investigates the areas below, which is a different question from what SS-31 will do for anyone, a claim about a living system that nothing on this site is sold for.
What it is. A man-made four-building-block peptide that gathers in mitochondria, also published as elamipretide.
What the research looks at. Animal and clinical-stage research on mitochondria and on cardiolipin.
How it is thought to work. Described in the research as sticking to cardiolipin, a fat molecule in the inner membrane of mitochondria. Its alternating pattern of bulky and positively charged building blocks is the feature associated with it ending up there.
What is not established. No approved product. SS-31 and elamipretide are two names for the same peptide, and certificates may use either; that is a naming difference, not a chemical one.
The full record, including the certificate for the lot in stock, is on the SS-31 product page.
Common questions
Does an SS-31 certificate showing 99% HPLC purity mean the vial is 99% SS-31 by mass?
Can mass spectrometry confirm that position one is D-arginine?
The certificate lists no counterion or water content. What should I assume?
How do I verify a certificate without relying on the seller?
The test date is more than a year before my shipment. Is the certificate still valid?
More documentation guides
Sources
- USP General Chapter <621> Chromatography. Establishes how a chromatographic procedure must be specified and how system suitability is demonstrated; supports the position that a purity percentage without column, gradient and detection wavelength is not reproducible.
- USP General Chapter <1225> Validation of Compendial Procedures. Defines specificity, accuracy and precision expectations for analytical procedures; supports the distinction between a method that has been validated and a number that has been reported.
- ICH Q3A(R2), Impurities in New Drug Substances. Source of the reporting, identification and qualification threshold concept applied here by analogy to unidentified peaks on a research-grade peptide chromatogram.
- PubChem entry for elamipretide. Public chemical record for molecular formula, molecular weight and the synonym set linking SS-31, MTP-131 and elamipretide; the place to check any CAS number before relying on it.
