The specifics, since they change the answer: BCH · Shanghai Sigma-Audley.
Both of these get recommended confidently by different people, which suggests neither is obviously right.
My constraints are cost, measurement resolution and how much handling I am prepared to do — in roughly that order.
What is the actual trade-off, and does it matter at the scale I am working at?
This is the question where methodology matters more than the conclusion.
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.
| Observation | Implication | How to check |
|---|---|---|
| Lot number not on the vial | Certificate cannot be tied to your material | Photograph vial and certificate together |
| No method section | The number is not reproducible | Request column, gradient, wavelength |
| Purity to two decimals, no chromatogram | False precision | Request the trace |
| Test date before manufacture date | Certificate belongs to a different lot | Compare dates |
| Identical figures across lots | One certificate reused | Compare two lots side by side |
| “Sterile filtered” with no sterility test | Process claim substituted for a result | Ask for the sterility report |
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.
Content assay results across the published datasets vary considerably more between suppliers than purity does, which makes content the more discriminating axis.
Compare content, not purity. Purity clusters and content does not.
Analytical standards and reagents with traceable certificates. Every quantitative result you read inherits the accuracy of the standard behind it.
Shop standardsAnswering 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.
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.
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 ratings on this site are a community opinion average on a ten-point scale and are not reconciled with any other community's figures.
Nothing here is medical advice, and research-use compounds are not approved for human use.
Use a fixed documentation checklist rather than an impression.
Start by asking what you are optimising for, because cost per milligram, documentation depth and lead time do not have a common winner.
Publish the method with the result. A comparison without the laboratory named and the submission dates given is not reproducible by anyone.
Mechanically, cost per milligram of actual peptide is the honest price comparison, which means dividing by measured content rather than by label claim.
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.
A single member running three suppliers on one method is worth more than thirty members running one supplier each.
Content is the more discriminating measurement than purity for supplier comparison, because purity clusters tightly among competent suppliers and content does not.
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 20 May 2024 by tobias_maartens — corrected a unit error in the worked example
Ratings on this site are ours alone and are deliberately not reconciled with anyone else's.
Sample size matters. One order each is an anecdote about six vials; three orders each over a year is the beginning of a comparison.
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.
No supplier on this site pays for its position, and the storefront links are marked nofollow and sponsored.
Name the laboratory and the dates or the comparison cannot be reproduced.
edited 5 Jun 2024 by tobias_maartens — added the citation requested in comments
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.