For reference: SWB · FGP · Japan.
I want to know what the trade-off actually is rather than which option is fashionable.
I would rather have a defensible reason than a marginal improvement.
Which axes does this decision turn on?
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.
Content is the more discriminating measurement than purity for supplier comparison, because purity clusters tightly among competent suppliers and content does not.
| 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 |
Publish the method with the result. A comparison without the laboratory named and the submission dates given is not reproducible by anyone.
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.
The caveat is that a comparison is a snapshot of the lots compared, and lots change.
One laboratory, one method, one submission. Otherwise it is not a comparison.
edited 29 Mar 2026 by forty_two_c — added the citation requested in comments
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 BiochemThe 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.
Cost per milligram of actual peptide is the honest price comparison, which means dividing by measured content rather than by label claim.
Mechanically, 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.
Name the laboratory and the dates or the comparison cannot be reproduced.
Start by asking what you are optimising for, because cost per milligram, documentation depth and lead time do not have a common winner.
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.
Sample size matters. One order each is an anecdote about six vials; three orders each over a year is the beginning of a comparison.
Price per milligram of measured peptide, not per milligram of label claim.
The part that matters: a single member running three suppliers on one method is worth more than thirty members running one supplier each.
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.
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.
Use a fixed documentation checklist rather than an impression.
The 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.
Compare content, not purity. Purity clusters and content does not.
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.