Knowing how to choose a research peptide vendor comes down to nine verifiable checks, and eight of them can be run before you place an order. The market is fragmented, documentation quality varies enormously, and the single most useful skill is knowing which claims can be tested against a document and which are decoration. This checklist is written for someone comparing two or three suppliers for laboratory reference material. Work through it in order — the early checks eliminate most candidates. Everything discussed concerns material supplied for research use only.
1. A lot-matched certificate of analysis, not a generic one
The document that matters names your lot number. A PDF headed with a product name and a purity figure but no lot, no analysis date and no batch size is a marketing asset, not a certificate. Ask for the COA for the lot you will receive, and check that the lot on the vial matches the lot on the paper when it arrives. Everything else on this list depends on this one working. The anatomy of the document is covered in how to read a peptide COA.
2. HPLC purity with the chromatogram attached
A number without a trace is unverifiable. A real reversed-phase HPLC report shows the chromatogram, the gradient conditions, the column, the detection wavelength (usually 214 nm for the peptide bond) and the integrated peak-area table. From the trace you can see whether the main peak is symmetric, whether impurities cluster near it — deletion sequences elute close to the target — and whether the integration excluded a solvent front that should have been counted. What the percentage does and does not mean is set out in HPLC purity explained.
3. Mass spectrometry identity confirmation
Purity says "one thing is present"; mass spectrometry says "the thing present has the expected mass". A COA reporting ≥99% purity with no MS data has established homogeneity without establishing identity, which is the weaker of the two claims. Expect an observed mass within a fraction of a dalton of theory for a small peptide, and see mass spectrometry and peptide identity for how to read the result.
4. Net peptide content and salt form — the check almost nobody runs
Synthetic peptides are isolated as salts. A vial labelled 10 mg contains 10 mg of powder, and that powder includes counter-ions (trifluoroacetate or acetate), residual water and residual solvent. Net peptide content — the fraction that is actually peptide — commonly runs 70–90% and is determined by amino-acid analysis or nitrogen determination. A vendor that will not state it is asking you to guess.
Worked example: real price per milligram
- Headline comparison. Vendor A: 5 mg at $60 = $12.00 per mg. Vendor B: 10 mg at $95 = $9.50 per mg. B looks 21% cheaper.
- Apply net peptide content. A discloses 92%: 5 × 0.92 = 4.6 mg of peptide, so $60 ÷ 4.6 = $13.04 per mg of peptide. B discloses 78%: 10 × 0.78 = 7.8 mg, so $95 ÷ 7.8 = $12.18 per mg.
- Result. B is still cheaper, but by 7% rather than 21% — and if B had not disclosed the figure at all, the comparison would have been fiction.
- Where it really bites. A molarity calculation run on label mass rather than net peptide content is wrong by the same 8–30%. For any quantitative work, this is a data-integrity issue, not a pricing one.
5. Third-party testing you can trace to a lot
"Third-party tested" is meaningful only if the third party is named, the report is dated, and the report cites the lot number. An independent laboratory report for a lot you cannot buy tells you the vendor once had a good batch. The mechanics — who the labs are, what they test, how to verify a report — are in third-party testing explained.
6. The specifications that match the claim being made
Different claims require different tests, and a COA should carry the ones the product's positioning implies.
| If the vendor claims… | Expect on the COA… | Red flag |
|---|---|---|
| ≥99% purity | HPLC chromatogram, gradient, wavelength, peak table | Number with no trace |
| Correct identity | MS with observed vs theoretical mass | Sequence restated as if it were a measurement |
| Known concentration achievable | Net peptide content, water content, counter-ion | Silence on salt form |
| Low endotoxin | LAL result in EU/mg | "Endotoxin free" with no assay |
| Sterile | Sterility test method and result | "Sterile-filtered" used as a synonym for sterile |
| Blend at a stated ratio | Per-component mass and purity — see blends vs single vials | One purity figure for a multi-component vial |
7. Range consistency and vial size sanity
A catalogue that offers the same molecule in 5, 10 and 20 mg vials with consistent specifications across all three is describing a real supply chain. A catalogue with hundreds of exotic sequences all listed as in stock, all at ≥99%, all in one vial size, is usually describing a drop-ship arrangement in which no one has handled the material. Size laddering also matters practically: vial sizes should let you reconstitute to a working concentration without absurd diluent volumes, as covered in reconstitution math.
8. How the vendor talks about use
This is a compliance check and a competence check at once. A supplier of research material describes research material: no human protocols, no titration schedules, no before-and-after imagery, no claims to treat or prevent anything, and clear research-use-only labelling on product pages and packaging. A vendor that publishes human usage guidance has told you it is not operating as a research supplier, and that its documentation practices may be similarly informal. The regulatory background is in what research use only means.
9. Logistics, support and what happens when something goes wrong
- Stock location and transit time. Domestic stock shortens transit and removes customs variability. Format matters more than speed for lyophilized powder — see shipping and cold chain.
- Packaging. Vials should arrive individually protected. Glass breakage is a packaging decision, not bad luck.
- Replacement policy for damaged or mismatched lots, stated before purchase rather than negotiated after.
- A technical contact who can answer a COA question. Send one before ordering; the quality of the answer is the most informative signal on this list.
- Lot retention. Vendors that retain samples can re-test a disputed lot. Vendors that cannot, cannot.
How to choose a research peptide vendor: scoring the checklist
Checks 1–4 are pass/fail: a supplier that cannot produce a lot-matched COA with a chromatogram, an MS result and a net peptide content figure should not be used for quantitative work regardless of price. Checks 5–7 differentiate good suppliers from adequate ones. Checks 8–9 predict what the relationship will be like once something goes wrong, which it eventually will.
Our own documentation practice — lot-matched COAs, HPLC and MS on every lot, stated purity thresholds and format-specific specifications — is applied across the full catalogue. Related reading: the purity, COA and testing FAQ.