The case in front of me: list of related substances · GGPeps.
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 can I legitimately conclude from this figure?
What makes a certificate useful is not its appearance but whether you could hand it to another laboratory and they would reproduce the result.
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.
Test results from a material supplier are different from independent results in ways that matter for interpretation, even if both are accurate.
Pharmacopoeial standards require method validation steps that research-grade certificates almost never claim to meet, and the absence of that claim is itself information.
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.
HPLC purity, identity confirmation and quantified content on the vial you actually hold. Reports arrive with the chromatogram attached, not just a number.
Submit a sampleFounded 1998. ISO 9001 and cGMP certified, 1,500+ staff and 200+ patents. The synthesis house behind a great many of the vials that get sent out for testing - batch-specific documentation with every order.
Visit GL BiochemA certificate without a method section is giving you a claim rather than a measurement, and claims are not evidence.
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 method section that differs markedly from pharmacopoeial standards is either innovative or nonstandard, and distinguishing the two requires expertise.
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.
The practical summary: check the lot number, ask for the method, and reserve judgement until you have both.
edited 11 May 2024 by label_claim — added a caveat about sampling
To be exact about it, 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.
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.
Worth being precise here: 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 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.
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.
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.
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.
Start from what the certificate claims to measure and what the claimed measurement actually answers, because those are two different questions.
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 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.
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.