Concretely: semaglutide · 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.
What would I need in addition before this supported a decision?
More usefully, a 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.
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 |
Worth being precise here: test results from a material supplier are different from independent results in ways that matter for interpretation, even if both are accurate.
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.
One qualification: a single result from a single vial at a single time is a point estimate with no error bar, and no amount of decimal places changes that.
If the certificate does not trace to your vial, it is not evidence about your vial.
Aggregated, published test results and vendor ratings built from submitted batches. Methodology stated, dataset browsable, no listing fees.
Browse resultsSpecifically, the most common trap is reading a certificate as if it were a guarantee when it is actually a single point estimate from a single test.
The field you have least reason to trust is the one that looks most impressive, because appearance and accuracy are not correlated.
On the detail: writing the lot number on your vial in permanent marker is worth doing because it later proves that the certificate traces to your material.
Worth noting that none of this is medical advice, and a compound sold for research use carries no regulatory approval in any jurisdiction.
The practical summary: check the lot number, ask for the method, and reserve judgement until you have both.
More usefully, start from what the certificate claims to measure and what the claimed measurement actually answers, because those are two different questions.
A method section that differs markedly from pharmacopoeial standards is either innovative or nonstandard, and distinguishing the two requires expertise.
Concretely, 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.
Industry guidance on this topic is consistent because it comes from first principles rather than convention.
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.
My working rule is that a document without a lot number, a method section and a test date is marketing.
Most certificates are written to look impressive rather than to be informative, and it is worth being sceptical of that gap.
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.
Ask whether the certificate answers the question you are actually asking, because the answer is often no.
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.
The practical summary: check the lot number, ask for the method, and reserve judgement until you have both.
edited 13 Jun 2025 by deamidation_watch — removed a claim I could not source
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.