Outright counterfeiting, where a vial contains something deliberately different from its label, is less common in research supply than mislabelling, where the vial contains roughly what it says but the documentation does not establish it. The second is far more frequent and is the one worth building checks around.
The check that settles it
Take the code printed on the certificate to the laboratory that issued it and ask them to confirm the document exists and matches. A fabricated certificate can be internally perfect. It cannot make the issuing laboratory agree it is real.
Everything below is detail around that single step, useful when it is unavailable or as a first pass.
| Check | What it proves | Effort |
|---|---|---|
| Confirm the code with the issuing laboratory | The document is genuine | One email |
| Lot on certificate matches lot on vial | The document describes your material | Seconds |
| Dates run forwards, with a plausible gap | Testing actually took time | Seconds |
| A method is named for every result | Results are measurements, not numbers | One minute |
| Reported mass reconciles with the formula | The compound is what it claims | Two minutes |
| Limits written as limits | The laboratory is being precise | Seconds |
| Figures vary across lots | Documents were produced, not templated | A few lots |
Ordered by how much each one establishes, not by how long it takes.
Reconciling the mass is the strongest desk check
A certificate reporting identity by mass states a number, and that number is predictable from the compound's formula. Sum the residue masses of the sequence, add one water, and compare. A mass that cannot be reconciled by any ordinary modification is the most substantive thing a reader can find without equipment.
Two cautions. Compare average mass to average and monoisotopic to monoisotopic, because mixing them produces a fraction-of-a-Dalton gap that looks like a finding. And end modifications such as an acetyl group shift the number legitimately. Molecular weight for buyers works through the arithmetic.
Be suspicious of uniformity, not of untidiness
The pattern worth distrusting is not sloppiness. It is sameness: identical purity figures across unrelated compounds, the same issue date on everything, no instrument named, no reporting limits anywhere, and turnaround identical for tests that take different lengths of time.
Real laboratory output is lumpy, because different assays behave differently and different months have different workloads. The lumps are the evidence.
Physical signals, which are weaker than documentary ones
- A cake that does not match the compound's usual appearance is worth a question, though appearance varies legitimately.
- A label with no lot number cannot be tied to any document at all, which is a documentation failure rather than a counterfeiting signal.
- A closure that shows no resistance on first entry may simply have equalised, but combined with other signals it is worth noting. Vial closures covers what the seal should behave like.
- A mass or appearance that differs visibly between vials of the same lot is a real finding and worth raising immediately.
Where mislabelled material actually comes from
Rarely from deliberate substitution. The common routes are duller and more frequent: bulk material repackaged without lot-level records, a certificate carried over from a previous batch, a transcription error between the laboratory report and the published document, or stock held so long that the document on file describes a lot that has since been replaced.
All four produce the same symptom, which is a vial whose contents cannot be established from the paperwork. None of them requires anyone to have acted dishonestly, which is precisely why checking is a routine control rather than an accusation.
The checks worth building into receiving
Most of this belongs at the point material arrives, not at the point it is used, because that is when the shipment is still a single identifiable unit and the supplier conversation is easiest.
- Lot on the vial against lot on the certificate, every time, for every lot.
- Certificate code confirmed with the issuing laboratory for any new supplier, and periodically for an existing one.
- Vials within a lot compared against each other for fill and appearance.
- Anything that does not reconcile raised in writing before the material is put away, which receiving and inspecting a shipment covers.
What to do if something does not reconcile
Stop using the lot, photograph the vial and label, keep the packaging, and put the question to the supplier in writing. If the answer does not resolve it, independent testing settles it: identity by mass spectrometry answers what the compound is, which is the question at issue. Auditing a peptide supplier covers how a supplier's response to this kind of question is itself informative.
This sits inside the wider picture of what gets tested and why, which why peptide testing matters sets out across the whole analytical panel.