I have kept every message, invoice and document, which I gather is the useful habit.
I would rather be corrected now than propagate something wrong.
I am specifically not interested in a testimonial; I am interested in a measurement.
What would count as evidence here, and does it exist?
Answer first: vet the documentation before you vet the supplier, because documentation is the only thing you can assess before spending anything.
The pre-order sequence: request a lot-specific certificate for the exact line, check that it names a lot code rather than a batch family, check that it carries the column, gradient and detection wavelength, and check the analysis date is recent relative to the lot.
The post-arrival sequence: inspect before reconstitution, photograph anything unexpected, confirm the lot code is physically on the vial, and submit a sample to an independent laboratory before committing to a larger order.
Published inter-laboratory comparisons of peptide purity routinely find spreads of half a per cent to a per cent on identical material, which sets a realistic expectation for agreement.
Ask for the lot-specific certificate before ordering. It is free and it is decisive.
Aggregated, published test results and vendor ratings built from submitted batches. Methodology stated, dataset browsable, no listing fees.
Browse resultsThe short version: ask for the lot-specific certificate, check the method section, check the lot code ties to a vial, then spend a small amount and test it yourself.
Published third-party data on a named lot is worth more than any aggregate rating, because it is about a specific object rather than about an average of other people's objects.
Set your accept threshold before you see the result. Deciding after the number arrives is how thresholds become negotiable, and everybody does it unless they wrote it down first.
Purity by RP-HPLC and quantified content are separate measurements answering separate questions, and only the second one tells you how many milligrams are in the vial.
Two lots agreeing is worth more than one lot excelling.
Start with one request that costs nothing — a lot-specific certificate for the material you would actually be shipped — and read what comes back rather than whether something comes back.
Ask what happens if a result comes back outside specification. The answer is informative regardless of what it is, and the question itself tells you something about how it lands.
Independent submission costs a fraction of a mid-sized order at any of the services this community uses, and it converts an opinion into a number attached to your own material.
The independent testing services this community references — Janoshik, Medutest, PeptideMeter and VendorInvestigate — publish results that can be searched by supplier, compound and date, which makes prior lots checkable.
Small first order, independent submission, then scale. In that order.
Ask PeptideStack is a static archive. Posting is closed, but the norms are worth stating: answer the question that was asked, show your working, cite the trial or the certificate, and say plainly where the evidence runs out.