Documentation
Nine Checks Before You Buy From a Research Peptide Supplier
You can work through eight of the nine before spending anything. The first few filter out most suppliers, and check four is the one buyers routinely skip.
Selecting a research peptide supplier comes down to nine verifiable checks, and all but one can be done before you order. The market is fragmented and paperwork quality ranges from excellent to useless, so the key skill is separating claims you can confirm from a document from claims that are just decoration. This checklist is aimed at labs weighing up two or three possible sources of reference material. Work through it in order — most suppliers fall away in the first few steps. Everything below concerns research material for laboratory use.
1. A certificate tied to your lot, not a generic PDF
A COA counts only when it names your lot. A PDF that shows a product name and purity value but omits the lot number, the analysis date and the batch size is promotional material, not a certificate. Request the COA for the exact lot you will receive, and once the parcel arrives, check that the lot printed on the vial is the one printed on the certificate. All other checks on this page rely on that match. Our guide how to read a peptide COA walks through each section of the document.
2. HPLC purity backed by a visible chromatogram
A purity figure on its own cannot be checked. A proper reversed-phase HPLC report shows the chromatogram itself, the gradient program, the column used, the detection wavelength — normally 214 nm, where the amide backbone absorbs — and a table of integrated peak areas. From the trace you can judge whether the main peak is sharp and symmetrical, whether impurities crowd around it the way deletion sequences tend to, and whether a solvent front was excluded from integration when it should have been counted. The meaning and limits of the percentage are explained under HPLC purity explained.
3. Mass spectrometry proving identity
Purity says a single component dominates; mass spectrometry says that component has the right mass. A COA stating ≥99% purity with no MS result has shown the sample is homogeneous, not that it is the correct molecule — the less valuable claim. For short peptides the measured mass should lie within a fraction of a dalton of the calculated value; see consult mass spectrometry and peptide identity for how to read the data.
4. Net peptide content and salt form — the step most buyers skip
Synthetic peptides are obtained as salts. A vial marked 10 mg therefore contains 10 mg of solid material made up of peptide plus counter-ions (TFA or acetate), moisture and leftover solvent. The share that really is peptide — the net peptide content — is typically 70 to 90% and is determined by amino-acid analysis or by nitrogen measurement. If a supplier will not tell you the figure, you are left guessing.
Worked example: what a milligram of peptide really costs
- Label prices. Supplier A sells 5 mg for €60, i.e. €12.00 per mg; supplier B sells 10 mg for €95, i.e. €9.50 per mg — seemingly 21% less.
- Correct for net peptide content. A declares 92%, so the vial holds 4.6 mg of peptide (0.92 × 5), and €60 buys it at €13.04 per mg (60 ÷ 4.6). B declares 78%, so the vial holds 7.8 mg (0.78 × 10), priced at €12.18 per mg (95 ÷ 7.8).
- Result. B is still the cheaper option, though by 7% rather than 21% — and if B had refused to publish the figure, the comparison would have meant nothing.
- The bigger problem. Molar concentrations worked out from label mass rather than net peptide content are wrong by the same 8–30%. For quantitative experiments that is a data-quality issue, not a budgeting one.
5. Third-party testing traceable to a lot
"independently tested" means something only when the outside laboratory is named, the report has a date, and it quotes the lot number. A third-party report on a lot that is no longer for sale proves only that the supplier once possessed a good batch. For who these labs are, what they test and how a report can be checked, see third-party testing explained.
6. Tests appropriate to what the product claims
Each claim requires its own analyses, and the COA should contain the tests that the way the product is marketed implies.
7. Consistency across the range, and sensible vial sizes
A catalogue offering one molecule in 5, 10 and 20 mg vials, with matching specifications for each, reflects genuine stock. A catalogue offering hundreds of unusual sequences — every one in stock, every one ≥99%, every one in a single vial size — more often reflects drop-shipping in which nobody touches the product. Sensible size steps also matter in practice: they should allow you to reach a usable working concentration without absurd amounts of diluent, as the reconstitution arithmetic demonstrates.
8. The language the vendor uses about use
This one checks both regulatory discipline and expertise. A research supplier discusses its products only as research material: there are no human protocols, no titration plans, no before/after images and no promise to treat or prevent any condition. A seller that offers human-use guidance has shown you it is not really a research supplier, and hints that its paperwork may be just as careless.
9. Logistics, support and the response when something fails
- Stock location and delivery time. Stock held within the EU shortens delivery and avoids customs delays. For freeze-dried powder, packaging format matters more than speed; see shipping and cold chain.
- Packaging. Each vial should arrive individually protected; broken glass reflects a packaging decision rather than misfortune.
- A published policy for replacing broken or mismatched lots, available before you buy rather than argued over later.
- Technical support that can deal with a COA query. Test it with one question before your first order — how well they answer tells you more than anything else here.
- Retained lot samples. A supplier that keeps retains can retest a lot when there is a dispute; one that does not, cannot.
Scoring the checklist
Checks 1 to 4 are pass/fail: if a supplier cannot provide a lot-specific COA with a chromatogram, a mass-spec result and a stated net peptide content, do not use it for quantitative experiments, whatever the price. Checks 5 to 7 distinguish strong suppliers from acceptable ones. Checks 8 and 9 show how the partnership will hold up when a problem eventually occurs, which sooner or later it will.
We follow the same documentation standard across the whole catalogue: lot-specific COAs, HPLC plus MS for each lot, declared purity limits, and specifications tailored to each format. See also the FAQ on purity, COAs and testing.
Questions
Which check matters most?
Obtaining a COA that refers to the specific lot that will be shipped to you. A PDF showing only a product name and a purity value — without a lot number, a date of analysis or a batch reference — cannot be linked to the vial on your bench, and every other check assumes that link exists.
What does net peptide content mean, and how does it affect price?
Synthetic peptides leave purification as salts, so a vial labelled 10 mg contains 10 mg of powder that also includes counter-ions, leftover moisture and traces of solvent. The fraction that actually is peptide — the net peptide content — commonly sits between 70 and 90%. If it is 78%, the 10 mg vial holds 7.8 mg of peptide, and a €95 price becomes €12.18 per milligram of real peptide instead of the €9.50 the label implies.
Is a purity number sufficient without the trace?
No. A purity percentage is the result of peak integration, and unless you see the chromatogram you cannot tell whether the main peak is sharp and symmetrical, whether closely eluting impurities such as deletion sequences are hiding under its flanks, or whether the solvent front was handled properly. Request the trace plus the method details: gradient, column type and the wavelength used for detection.
Does high purity guarantee the right peptide?
No. Purity tells you one component dominates the sample, not what that component is. Identity is established by mass spectrometry, which compares the measured mass with the theoretical one. A COA that reports 99% purity without any mass-spec result has proven only homogeneity — the less important of the two claims.
How can a third-party testing claim be verified?
Such a claim counts only if the outside lab is identified by name, the report carries a date, and it lists the same lot number you are buying. A report on a batch that has sold out shows nothing more than that the supplier had one good lot at some point. Ask for the report on your lot and check that its results match the supplier's own COA.
What can a supplier's marketing copy tell me?
Genuine research suppliers talk only about laboratory use: you will find no human protocols, no titration plans, no treatment promises and no before/after pictures on their pages. A seller that publishes human-use advice has effectively admitted it is not acting as a research supplier — and relaxed compliance usually goes hand in hand with relaxed paperwork.
Is a very large catalogue reassuring?
Not on its own. Hundreds of rare sequences, all apparently in stock, all at the same purity and all in one vial size, typically indicate drop-shipping, where no one in the chain has actually handled the product. A single molecule offered in several vial sizes with matching specifications says more about a real supply chain than catalogue size does.
Which question should I put to a supplier before I order?
Send one precise technical question about a specific COA — for example, what the counter-ion and net peptide content are for a given lot. The speed, precision and correctness of the reply is a good preview of the help you will get if a parcel turns up broken or the lot on the vial does not match the paperwork.