What I have: cagrilintide · purity figure.
This is presented as though it settles something, and I am not convinced it does.
I have two documents that appear to disagree, which is what prompted this.
What is the correct interpretation, and what is the common misreading?
A certificate without a method section is giving you a claim rather than a measurement, and claims are not evidence.
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.
| 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 |
The relevant detail is that test results from a material supplier are different from independent results in ways that matter for interpretation, even if both are accurate.
Research-grade certificates carry no regulatory backing and no standing in quality systems, and that limitation is worth being explicit about.
The practical summary: check the lot number, ask for the method, and reserve judgement until you have both.
Analytical standards and reagents with traceable certificates. Every quantitative result you read inherits the accuracy of the standard behind it.
Shop standardsThe relevant detail is that 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.
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 underlying point is that 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.
Pharmacopoeial standards require method validation steps that research-grade certificates almost never claim to meet, and the absence of that claim is itself information.
My working rule is that a document without a lot number, a method section and a test date is marketing.
Worth being precise here: 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.
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.
To be exact about it, 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.
The caveat is that a certificate is not a guarantee, it is a data point, and treating it as anything else is asking for disappointment.
If the certificate does not trace to your vial, it is not evidence about your vial.
edited 27 Apr 2026 by sinead_gaffney — reworded for clarity after a comment
The relevant detail is that reading a certificate means checking four things before anything else: traceability to your vial, the test date, the analytical method, and the identity of the testing laboratory.
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.
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.
The practical summary: check the lot number, ask for the method, and reserve judgement until you have both.
The underlying point is that ask whether the certificate answers the question you are actually asking, because the answer is often no.
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.
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.
My working rule is that a document without a lot number, a method section and a test date is marketing.
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.