Setup, so nobody has to ask: survodutide · date of analysis.
The figures are clear enough; the question is what they mean and what they do not.
I can supply the numbers if the specifics change the answer.
How should I read this, and where are the traps?
Start from what the certificate claims to measure and what the claimed measurement actually answers, because those are two different questions.
Multiple testing on the same lot reported in a single document suggests internal quality control; identical figures across different lots suggests the same certificate reused.
| Δ mass (Da) | Most likely cause | Distinguishing feature |
|---|---|---|
| +1 | Deamidation (Asn or Gln) | New peak, slightly earlier retention |
| −17 | Loss of ammonia | Often with deamidation |
| −18 | Dehydration / succinimide | pH-dependent, reversible |
| +16 | Oxidation (Met, Trp) | Earlier retention, light-related |
| −128 | Missing Gln or Lys | Deletion sequence from synthesis |
| 0 | Isomer: racemisation or scrambling | Same mass, shifted retention |
Writing the lot number on your vial in permanent marker is worth doing because it later proves that the certificate traces to your material.
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.
Worth noting that none of this is medical advice, and a compound sold for research use carries no regulatory approval in any jurisdiction.
If the certificate does not trace to your vial, it is not evidence about your vial.
Analytical standards and reagents with traceable certificates. Every quantitative result you read inherits the accuracy of the standard behind it.
Shop standardsMechanically, the certificate is not the answer to your question; it is a data point that you need to combine with other information to build an answer.
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.
More usefully, 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.
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.
The practical summary: check the lot number, ask for the method, and reserve judgement until you have both.
edited 31 Oct 2024 by wren_calloway — fixed an arithmetic slip in the third paragraph
The relevant detail is that a certificate without a method section is giving you a claim rather than a measurement, and claims are not evidence.
Test results from a material supplier are different from independent results in ways that matter for interpretation, even if both are accurate.
Put another way, 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.
Industry guidance on this topic is consistent because it comes from first principles rather than convention.
My working rule is that a document without a lot number, a method section and a test date is marketing.
Ask whether the certificate answers the question you are actually asking, because the answer is often no.
The test date matters because a certificate six months older than the vial is not evidence about your material, it is evidence about what the material was like half a year ago.
The limitation is cost — truly rigorous testing on every lot is expensive enough that most people do not do it, which is exactly why the variation matters.
If you only pay for one test, pay for quantified content. Purity is the number everyone quotes and content is the number that changes what you do.
The certificate is only as useful as the lot number, because without traceability it is gossip about someone else's material.
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.
Research-grade certificates carry no regulatory backing and no standing in quality systems, and that limitation is worth being explicit about.
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.
In practice: ask for the chromatogram, check the method section, check the lot number against the vial, and set your accept threshold before you see the result rather than after.
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.