A MOTS-c certificate of analysis is read backwards from the lot number. Confirm the lot on the document matches the vial, then check that identity was established by mass spectrometry against the 16-residue sequence, that purity carries a named RP-HPLC method, and that net peptide content is stated separately from gross fill.
- MOTS-c (Human) is a 16-residue mitochondrial-derived peptide, sequence MRWQEMGYIFYPRKLR, formula C101H152N28O22S2, average mass 2174.6 g/mol.
- A certificate describes one lot on one date; if the lot number does not match the vial label, the document describes different material.
- Mass spectrometry establishes composition consistent with the claimed sequence, not residue order, because leucine and isoleucine are isobaric.
- RP-HPLC purity is area percent at a specific wavelength and excludes salt, water, residual solvent and anything that fails to elute.
- Net peptide content for a TFA salt of this basic sequence typically falls between 70 and 85 percent of gross vial mass.
- No approved medicine contains MOTS-c and no USP monograph exists, so every reported purity figure rests on a method the testing laboratory chose.
What the document actually claims
A certificate of analysis is a report on tests performed on one lot of material, on a stated date, by a stated laboratory, using stated methods. That is the whole of it. It is not a warranty, not a statement about the next lot, and not evidence that the vial in your hand came from the lot described. Every one of those gaps has to be closed by something outside the PDF.
Two documents get called the same thing and are not. A manufacturer's in-house CoA is generated by the people who made the material. A third-party test report is generated by a laboratory with no commercial interest in the result. Both can be honest and both can be worthless; the difference is where the incentive sits, and a reader should know which one is on the screen before assessing anything else on it. Many suppliers publish both, with the in-house sheet carrying the full field set and the third-party report carrying only identity and purity.
MOTS-c is a useful case for teaching CoA literacy because the molecule is small, well described in the literature, and cheap enough to synthesize that the documentation is often the only thing distinguishing one offering from another. The chemistry is unambiguous. The paperwork is where the variance lives.
- Lot number against the vial label — first, always
- Printed sequence, so identity can be checked at all
- Identity method: mass observed, tolerance, instrument
- Purity method: column, gradient, wavelength, not just a number
- Net peptide content and counterion — the mass you actually have
- Test date, issuing laboratory, and confirmation from the lab itself
Start with the lot number, not the purity figure
The purity figure is the first thing everyone looks at and close to the last thing that matters. Begin with lot identity, because if the lot on the certificate does not match the lot on the vial label, nothing further on the page describes your material.
Check three things in this order. The lot or batch string on the certificate character for character against the vial label, including leading zeros and separators. The product name and, where given, the catalog number. Then the quantity per vial, which should agree with what you ordered and with what the vial says.
A generic certificate is one that carries no lot number at all, or carries a lot number that appears on every certificate the supplier publishes for that product. This is common. It usually means the supplier tested one batch at some point and has been circulating the same file since. The document may be a genuine test report on a genuine batch, and it still tells you nothing about the powder you received. Ask for the lot-specific sheet, and treat an inability to produce one as a finding rather than an inconvenience.
Where the vial label carries a lot and the certificate carries a different one, that is not a clerical detail to be waved through. Record it, stop, and query it before the material enters any protocol.
Identity: what the mass spectrum proves and what it does not
MOTS-c (Human) is a 16-residue peptide encoded within the mitochondrial 12S rRNA region, described by Lee and colleagues in Cell Metabolism in 2015. The sequence in one-letter code is MRWQEMGYIFYPRKLR, free acid at the C-terminus, no disulfides, no modifications. The free-base formula is C101H152N28O22S2, average mass 2174.6 g/mol, monoisotopic mass 2173.11.
A competent certificate prints the sequence. A name alone is not identity, and the parenthetical (Human) in a catalog title is a species designation that a reader should be able to verify against the printed residues rather than accept on trust. If the sequence is absent from the document, you cannot check that the mass reported is the mass of the peptide you ordered.
Now the limit. Electrospray or MALDI mass spectrometry measures mass. Mass is a function of composition, not order. Two of the residues here, leucine and isoleucine, are isobaric, and any transposition of residues anywhere in the chain leaves the mass untouched. An MS identity result therefore establishes that the material has a composition consistent with the claimed sequence. Sequence order requires tandem MS with assigned fragment ions, or amino acid analysis combined with a sequencing method. Almost no research-grade certificate carries that, and the honest way to read a mass-only identity line is as a strong but incomplete check.
The average-versus-monoisotopic gap of about 1.5 Da causes more confusion than it should. A low-resolution instrument reports the average; a high-resolution instrument reports the monoisotopic peak. A certificate quoting 2173.1 and one quoting 2174.6 can both be correct.
| Species or shift | Value | What it indicates |
|---|---|---|
| Neutral, free base | 2174.6 (mono 2173.11) | Intact peptide |
| [M+H]+ | 2175.6 | Singly protonated |
| [M+2H]2+ | 1088.3 | Common base peak in ESI |
| [M+3H]3+ | 725.9 | Four basic sites support high charge states |
| +16 Da | 2190.6 | Oxidation at one of the two methionines or the tryptophan |
| +32 Da | 2206.6 | Double oxidation |
| +0.98 Da | 2175.6 neutral | Deamidation of the single glutamine; needs high resolution to see |
| −156.2 Da | 2018.4 | Loss of a C-terminal arginine, a synthesis truncation |
Two methionines and a tryptophan in a sixteen-residue chain make this sequence unusually oxidation-prone for its size. If the spectrum on the certificate is reproduced as an image, look for a +16 satellite. It is frequently there and frequently unremarked.
Purity: the number is uninterpretable without the method
A purity claim of 99% means nothing until you know what was separated, how, and what the detector was watching. The standard technique is reversed-phase HPLC with UV detection, and a usable certificate names at minimum the column chemistry and dimensions, the mobile phase composition, the gradient, the flow rate, the run time, the detection wavelength, and the injection amount. The result is reported as area percent of the main peak.
Detection wavelength deserves attention. Peptide work is normally done at 214 to 220 nm, where the amide bond absorbs and every peptidic species in the sample is visible in rough proportion to its bond count. A certificate reporting purity at 280 nm is measuring aromatic absorbance instead, which for MOTS-c means tryptophan and two tyrosines. Impurities lacking those residues are dim or invisible at that wavelength, and the number comes out flattering. This is not necessarily deceptive. It is sometimes just a method inherited from protein work. Either way it changes what the figure means.
Area percent is not mass percent, and it is not a measure of everything in the vial. Anything that does not elute within the gradient does not appear. Anything without a chromophore at the detection wavelength does not appear. Salts, residual solvents, water and endotoxin are separate determinations with separate methods, and their absence from the certificate means they were not tested, not that they were absent from the powder.
USP General Chapter <621> sets out the system suitability requirements a chromatographic procedure has to meet before its results are considered valid: resolution, tailing factor, repeatability, theoretical plates. A certificate that reports a purity figure without any system suitability data is asking you to accept a measurement whose reliability was not demonstrated. Most research-grade certificates do exactly that. It is worth knowing that this is the compromise you are making.
Net peptide content, gross fill, and the counterion
This is the field most often missing and the one with the largest effect on what you actually received. Chromatographic purity describes the proportion of peptide-related material that is the target peptide. Net peptide content describes what fraction of the powder in the vial is peptide at all. They are different questions and a lot can score well on the first while the second is unstated.
Solid-phase synthesis followed by preparative RP-HPLC in trifluoroacetic acid leaves the peptide as a TFA salt. MOTS-c carries three arginines and one lysine, so up to four TFA counterions can associate with each molecule. Water is also present, taken up during and after lyophilization, and a hygroscopic peptide powder can hold several percent by mass.
The arithmetic, using four TFA as the worst case:
4 × 114.02 = 456.1 g/mol of counterion
2174.6 ÷ (2174.6 + 456.1) = 0.827, or 82.7% peptide
Subtract three to five percent water and the ceiling drops toward 78 to 80%. Real net content figures for basic peptides of this class commonly land between 70 and 85%. So a 10 mg vial with a net peptide content of 78% contains:
10 mg × 0.78 = 7.8 mg of peptide
Net content is determined by quantitative amino acid analysis or by nitrogen determination, and TFA is quantified by ion chromatography or fluorine NMR. If the certificate reports none of these, the vial mass is a gross fill weight and the peptide mass is unknown. That matters for any concentration you calculate downstream and it matters for price comparison; the cost-per-mg tool gives a misleading answer if one supplier quotes net content and another quotes gross. The vial concentration calculator takes whichever figure you decide to work from, and the decision should be written down.
Field by field
| Field | Expected content | Common failure |
|---|---|---|
| Product name | MOTS-c (Human), with catalog number | Species qualifier omitted |
| Sequence | MRWQEMGYIFYPRKLR, one-letter code, termini stated | Absent, leaving identity uncheckable |
| Molecular formula and mass | C101H152N28O22S2; 2174.6 average, free base | Salt mass quoted without saying so |
| Lot or batch number | Alphanumeric string matching the vial label | Blank, or identical across every lot |
| Appearance | White to off-white lyophilized solid | Boilerplate never actually observed |
| Identity method and result | ESI-MS or MALDI-TOF, observed mass with tolerance | Result with no method named |
| Purity method and result | RP-HPLC area %, column, gradient, wavelength | Bare percentage; wavelength unstated |
| Net peptide content | % by AAA or nitrogen determination | Missing entirely |
| Counterion content | % TFA or acetate, method named | Missing entirely |
| Water content | % by Karl Fischer | Missing; matters for a hygroscopic solid |
| Quantity per vial | Fill weight, gross or net specified | Ambiguous which is meant |
| Date of manufacture | When the lot was made | Conflated with the test date |
| Date of analysis | When the reported tests were run | Absent, so age of the data is unknown |
| Issuing laboratory | Name, address, contact, accreditation scope | A logo and nothing else |
| Signature or approval | Named analyst or QC releaser | Unsigned, or an unattributed scrawl |
| Storage statement | Conditions the lot is expected to hold under | Copied from a different physical state |
The two date fields are worth separating deliberately. A lot manufactured in March and tested in March, shipped to you in November, has documentation eight months older than the material in your protocol. That is not a defect. It is a fact about the age of the evidence, and the record should carry it. Our own quality standard page sets out which of these fields we consider non-optional.
Verify the document at the laboratory, not with the seller
A PDF is trivially editable. Purity figures get raised, lot numbers get changed, laboratory letterheads get lifted from a real report onto a fabricated one. None of this requires skill. The consequence is that a certificate has evidentiary weight only after the issuing laboratory confirms it issued that document, for that lot, with those results.
The verification is short. Find the laboratory independently, through its own website or a public accreditation register, and do not use the phone number or email address printed on the certificate you are checking. Contact them with the report number and the lot identifier and ask whether the document exists in their records and whether the reported values match. Many contract laboratories will answer a straightforward query of this kind, and some run a public portal keyed to report numbers.
Check the accreditation claim while you are there. ISO/IEC 17025 accreditation is granted for a specific scope of methods, and a laboratory accredited for elemental analysis is not thereby accredited for peptide chromatography. Accreditation bodies publish searchable scope documents. A certificate carrying an accreditation logo for work outside the accredited scope is making an implication the accreditation does not support.
Smaller checks that take a minute each: open the PDF properties and look at the creation software and author field, since a report authored in a consumer image editor is a signal; look for a digital signature; compare fonts and alignment across the page for the patchwork appearance of pasted text. And keep the certificates you receive over time. A supplier whose every lot returns 99.2% purity for two years is reporting a number that no synthesis campaign produces naturally.
Where the material matters to a result you intend to publish, the resolution is independent testing. Send a retained aliquot to a contract laboratory and compare their report to the supplier's. It costs less than repeating a failed study.
What certificates for this compound usually leave out
Sterility and endotoxin are almost never on a research peptide certificate, and they should not be assumed. Lyophilized powder produced for laboratory use is not manufactured under sterility assurance and no line on the document implies otherwise. If a protocol requires low endotoxin, that is a separate specification to request in advance and a separate test to pay for.
Residual solvent testing is similarly rare. Synthesis and purification involve dimethylformamide, dichloromethane, acetonitrile, piperidine and others, and while lyophilization removes most of what remains, ICH Q3C classifies these solvents by toxicity and sets limits for pharmaceutical products. A research certificate silent on solvents is silent because nobody measured them.
Stability data is the third absence. A storage recommendation printed on a certificate is usually a convention rather than a conclusion from a study on that lot. A real expiry or retest date requires stability work in that container under those conditions, and for a research peptide it generally has not been done. Treat an unqualified shelf-life claim with the same reserve you would apply to a purity figure with no method behind it. Once material is dissolved, the clock changes character entirely, which is a separate topic covered in our note on diluent selection and documentation.
One genuine sequence complication is worth flagging. A mitochondrial polymorphism at m.1382A>C, reported in East Asian population studies, produces a K14Q variant of MOTS-c. Catalog material is the reference sequence, and a certificate printing the residues lets you confirm that rather than infer it. This is the kind of thing a printed sequence resolves in five seconds and a product name never resolves at all.
Regulatory position
MOTS-c holds no marketing authorisation from the FDA, the EMA, or any comparable regulator. There is no approved product, no monograph in USP–NF establishing a compendial identity or purity procedure for it, and consequently no reference standard against which a supplier's method can be benchmarked. Every purity figure you read for this compound comes from a method the testing laboratory chose for itself.
Substances without approval for human therapeutic use fall under category S0 of the World Anti-Doping Agency Prohibited List. Readers with anti-doping obligations should check the current List directly rather than rely on a secondary summary, since the categories are revised annually.
Status verified 26 August 2026.
FOR LABORATORY AND IN-VITRO RESEARCH USE ONLY. NOT FOR HUMAN OR ANIMAL CONSUMPTION. NOT FOR PERSONAL, MEDICAL, DIAGNOSTIC, THERAPEUTIC, OR RECREATIONAL USE.
The absence of a compendial standard is the reason CoA literacy carries so much weight here. With an approved drug substance, the pharmacopoeia defines the test and the acceptance criteria and the argument is only about whether the lot passed. With MOTS-c, the supplier defines the test as well, and a reader who does not check the method is accepting both halves of the claim on trust.
Common questions
Is 99% purity on a MOTS-c certificate a good result?
Why does the certificate quote two different molecular weights?
What does net peptide content change in practice?
How do I confirm the certificate is genuine?
Should identity be established by mass spectrometry alone?
Why do certificates rarely include sterility or endotoxin data?
More documentation guides
Sources
- Lee et al., Cell Metabolism, 2015. Original identification and characterization of MOTS-c as a 16-amino-acid peptide encoded within the mitochondrial 12S rRNA region; supports the sequence and origin stated here.
- USP General Chapter <621>, Chromatography. Defines system suitability parameters including resolution, tailing factor and repeatability that a chromatographic purity determination must satisfy before its result is considered valid.
- ICH Q2(R2), Validation of Analytical Procedures. Establishes the validation characteristics an analytical procedure is expected to demonstrate; the reference point for judging whether a certificate names enough about its methods.
- ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories. Accreditation is granted against a defined scope of methods; supports the point that a logo alone does not establish competence for peptide chromatography.
