A supplier evaluation is usually conducted backwards: an order is placed, the material arrives, and the questions start when something looks wrong. Running the questions first costs an afternoon and is the cheapest quality control available.
What follows is organised by what each section actually tests, since the point is not to collect answers but to find out what a supplier knows about its own process.
Documentation
- Is a lot-specific certificate of analysis provided as standard, without being requested?
- Can a certificate be reviewed before ordering rather than after?
- Does the certificate carry a lot number that appears on the vial label?
- Are the underlying chromatograms and spectra available, or only the summary figures?
- How long are records retained, and can a certificate be reissued for a past lot?
That last question is more diagnostic than it looks. A supplier that cannot retrieve documentation for material sold a year ago does not have a record system; it has a document generator.
Analytical scope
- Which assays are run on every lot, and which are periodic or skipped?
- At what wavelength and under what gradient is purity determined?
- Is identity confirmed by mass spectrometry with an observed value reported?
- Is net peptide content determined, and by what method?
- Are endotoxin and sterility tested, and by which compendial methods?
- Are elemental impurities and residual solvents assessed?
The distinction between every-lot and periodic testing is where the real differences sit. Two suppliers can list the same assays while one runs them on each batch and the other ran them once on a representative lot.
Independence
- Is testing performed in-house, by a third party, or both?
- Where third-party, is the laboratory accredited, and to which standard and scope?
- Does the certificate identify the testing laboratory?
In-house testing is not inferior by definition, and a well-run internal laboratory can be excellent. The point is knowing which it is, because independent confirmation and self-reported results carry different weight.
Manufacturing
- Where is synthesis performed, and is it the supplier's facility or a contract manufacturer?
- Is the same source used consistently, or does it vary by lot and availability?
- What quality framework does the facility operate under?
- Is material filled and finished at the same site, or shipped in bulk and repackaged?
Repackaging is common and unremarkable, but it introduces a step where identity and labelling can diverge, so it is worth knowing whether it happens and under what controls.
Logistics
- How is material shipped, with what coolant, and qualified for what duration?
- Are temperature indicators or data loggers included?
- What is the process when a shipment arrives outside specification?
- What are typical processing and transit times, and what is the stated cutoff?
Commercial terms
- What is the published return and refund position, and what is the window?
- Is pricing transparent, or quoted case by case?
- Are core catalogue items held in stock, and what is the backorder position?
- Is there a named contact, and what is the response time in practice?
Answers that should end the conversation
A handful of responses are disqualifying rather than merely disappointing.
- A certificate of analysis supplied without a lot number, or one that cannot be matched to the vial.
- A refusal to provide documentation before an order is placed.
- A purity claim with no method behind it, or a certificate that is visibly a template with values typed in.
- Marketing that describes outcomes in people, which indicates a supplier operating inconsistently with the designation its products carry.
- An inability to say where material is manufactured.
Running it in practice
The questions do not need to be asked as an interrogation. Sending the list and asking for written answers is normal procurement practice and is also informative in itself: how quickly and how specifically a supplier replies tells you most of what the answers would.
Keep the responses. They become the baseline against which a later discrepancy is assessed, and they are the record that shows the choice of supplier was a decision rather than an accident.
This sits inside the wider picture of what gets tested and why, which why peptide testing matters sets out across the whole analytical panel.