What I have: a sterility test · dimerisation · tirzepatide.
I have used one of these for a while and I am considering switching, which requires a reason.
What I care about is reproducibility, because a result I cannot repeat is not useful to me.
What does each option buy me, and what does it cost me?
Specifically, what a useful certificate carries is debatable, but there are certain fields that almost no research-grade certificate includes despite their being standard in pharmaceutical work.
The certificate is a snapshot and nothing else — it tells you about the material on one day from one sample of one lot, and extrapolation beyond that requires logic.
| Test | Answers | Does NOT answer |
|---|---|---|
| RP-HPLC, area % | What fraction of detected material is the target | How much target is present |
| Quantified content | Milligrams of peptide per vial | What the impurities are |
| ESI-MS identity | Whether the molecular weight matches | Purity, or isomeric substitution |
| Peptide mapping | Sequence, localised to a fragment | Quantity |
| Karl Fischer | Water content of the solid | Solvent content |
| LAL endotoxin | Pyrogen load in EU/mg | Sterility |
| Sterility test | Growth in defined media over 14 days | Endotoxin, or bioburden count |
On the detail: comparison across certificates from different laboratories is almost never valid, even when the material is the same, because the methods are almost never the same.
Industry guidance on this topic is consistent because it comes from first principles rather than convention.
The practical summary: check the lot number, ask for the method, and reserve judgement until you have both.
Aggregated, published test results and vendor ratings built from submitted batches. Methodology stated, dataset browsable, no listing fees.
Browse resultsA useful certificate has five elements: the lot number, the analytical method, the reported result with units, the date of analysis, and the primary data or a reference to it.
Writing the lot number on your vial in permanent marker is worth doing because it later proves that the certificate traces to your material.
A purity figure to two decimal places with no supporting chromatogram is giving false precision and is a red flag on the same level as spelling errors.
Pharmacopoeial standards require method validation steps that research-grade certificates almost never claim to meet, and the absence of that claim is itself information.
If the certificate does not trace to your vial, it is not evidence about your vial.
Start from what the certificate claims to measure and what the claimed measurement actually answers, because those are two different questions.
Lot number visibility is the first check, and it is the one most certificates fail — the number is not printed on the vial, or it is on the certificate but the vial is unmarked.
More usefully, a method section that differs markedly from pharmacopoeial standards is either innovative or nonstandard, and distinguishing the two requires expertise.
Published inter-laboratory comparisons of the same material routinely find spreads of half a per cent to a full per cent, which sets realistic expectations.
My working rule is that a document without a lot number, a method section and a test date is marketing.
In practice, ask whether the certificate answers the question you are actually asking, because the answer is often no.
The laboratory name and accreditation status can be checked in real time against the testing service's own register, and that two-minute check catches substituted certificates.
The standards that exist in this space — ICH Q3A, Q3B and various pharmacopoeial chapters — are worth reading once even if nothing you test is obliged to meet them.
The practical summary: check the lot number, ask for the method, and reserve judgement until you have both.
edited 19 Jan 2025 by Dr_Priya_Raghunathan — removed a claim I could not source
Specifically, before anything else, check that the lot number on the certificate matches the vial in your hand — that traces back to your material and not to some other lot from some other date.
Batch versus lot is a semantic distinction that determines whether one certificate applies to ten vials or to one, and checking this distinction is worth a minute.
Be careful not to over-read this — a certificate that is imperfect is not worthless, it is just a starting point for thought rather than an endpoint.
If the certificate does not trace to your vial, it is not evidence about your vial.
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.