Details up front: SGN · Qingdao Sigma Chemical.
I have used one of these for a while and I am considering switching, which requires a reason.
What I care about is reproducibility, because a result I cannot repeat is not useful to me.
What does each option buy me, and what does it cost me?
Answer first: comparing suppliers is only meaningful if the comparison holds the laboratory, the method and the compound constant, and most published comparisons hold none of them.
To compare properly: order the same compound at the same nominal strength from each supplier, submit all samples to the same laboratory in the same submission if possible, and ask for the same test set on each.
| 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 |
On the detail: content is the more discriminating measurement than purity for supplier comparison, because purity clusters tightly among competent suppliers and content does not.
Content assay results across the published datasets vary considerably more between suppliers than purity does, which makes content the more discriminating axis.
Name the laboratory and the dates or the comparison cannot be reproduced.
Aggregated, published test results and vendor ratings built from submitted batches. Methodology stated, dataset browsable, no listing fees.
Browse resultsThe short version: same compound, same laboratory, same method, ideally same week — otherwise you are comparing laboratories rather than suppliers.
Lead time and lane behaviour are supplier properties too and are easier to compare than analytical ones, because they need no laboratory at all.
The underlying point is that sample size matters. One order each is an anecdote about six vials; three orders each over a year is the beginning of a comparison.
Gradient slope, column chemistry and detection wavelength all affect the reported purity figure, which is why the method section is the part that makes results comparable.
Price per milligram of measured peptide, not per milligram of label claim.
It helps to be literal here: ratings on this site are ours alone and are deliberately not reconciled with anyone else's.
Publish the method with the result. A comparison without the laboratory named and the submission dates given is not reproducible by anyone.
Compare documentation on a fixed checklist rather than by impression: lot specificity, method section, chromatogram availability, quantified content, water and counter-ion figures, and whether the code is on the vial.
Inter-laboratory spread on identical peptide material is routinely half a per cent to a per cent by RP-HPLC, which is the noise floor for any cross-laboratory comparison.
Compare content, not purity. Purity clusters and content does not.
Answering this needs the axis. A supplier that is best on paperwork and a supplier that is best on price are both correct answers to different questions.
Cost per milligram of actual peptide is the honest price comparison, which means dividing by measured content rather than by label claim.
The caveat is that a comparison is a snapshot of the lots compared, and lots change.
Use a fixed documentation checklist rather than an impression.
The relevant point is that two competent laboratories disagree by half a per cent on identical material, which is larger than most of the differences people argue about.
Submitting to different laboratories introduces a method difference that commonly exceeds the supplier difference. Gradient slope alone can move a reported purity figure by a per cent in either direction.
No supplier on this site pays for its position, and the storefront links are marked nofollow and sponsored.
One laboratory, one method, one submission. Otherwise it is not a comparison.
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.