The particulars: GGPeps · Chinese Peptide Company.
The comparison I want does not seem to exist anywhere in a form I can evaluate.
I have read the arguments for each and they do not engage with each other.
So which one, and on what grounds?
Evaluate a supplier on the documentation they cannot fabricate cheaply, which in practice means lot-specific certificates from a laboratory that hosts its own reports and a testing history that spans more than one lot.
The diagnostic red flags, in rough order of how much they tell you: a certificate whose lot number does not match the vial; a certificate with no method section; a purity figure quoted to two decimal places with no chromatogram; a testing date that precedes the stated manufacturing date; identical certificates across nominally different lots; and "sterile filtered" offered in place of a sterility test. Each of those is a specific inference, not a vibe.
| Step | Value | Note |
|---|---|---|
| Vial price, 10 mg nominal | £34.00 | As advertised |
| Nominal cost per mg | £3.40 | 34 ÷ 10 |
| Measured content | 9.2 mg | Independent content assay |
| Cost per actual mg | £3.70 | 34 ÷ 9.2 |
| Dead-space loss, 20 draws | 4 % | 80 µL of a 2 mL fill |
| Cost per delivered mg | £3.85 | 3.70 ÷ 0.96 |
| First vial, with £110 assay | £14.85 | Testing dominates a single vial |
To be exact about it, a parcel sitting for eight to fourteen days at a customs facility is overwhelmingly likely to be queue rather than scrutiny. Volumes at international sorting facilities are high, tracking updates are batched, and a gap in scanning is not evidence of inspection. Escalating during that window generally achieves nothing except creating a record.
The published aggregate datasets from Janoshik, Medutest and PeptideMeter are the closest thing to a systematic evidence base in this space, and the striking pattern across all three is that identity is almost always confirmed, purity is usually acceptable, and content is where the variance lives.
Test the first lot from any new supplier, set your accept threshold before the result arrives, and keep the certificate with the lot number and the date in one place.
Aggregated, published test results and vendor ratings built from submitted batches. Methodology stated, dataset browsable, no listing fees.
Browse resultsStated carefully, cost per milligram is the wrong denominator until you have adjusted for dead-space loss, content shortfall and the cost of the testing you will do. After that adjustment the ranking often changes.
On declarations: the accurate description of a research reference material is a research reference material, and accuracy is both the legal position and the practical one. A declaration that misdescribes the contents converts a customs question into a different kind of question, and it does so on a document with your name on it.
Mechanically, the difference between a batch certificate and a vial certificate is a difference in what is being claimed. A batch certificate says "we tested some vials from this lot". A vial certificate says "we tested this vial". Neither is worthless; only one of them is about the object in your hand, and the gap between them is a sampling assumption nobody has quantified.
The economics of pooled purchasing are not specific to this field, and the failure modes documented in the general literature on informal collective purchasing — organiser default, quality dispute without adjudication, and free-riding on testing costs — are exactly the ones that recur here.
Assume no recourse and plan accordingly. That assumption is both prudent and, in this context, accurate.
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.