The specifics, since they change the answer: SSA · HJ · the United States.
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?
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.
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.
More usefully, 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.
Comparisons drawn from different laboratories at different times are weaker evidence than most people treat them as.
One laboratory, one method, one submission. Otherwise it is not a comparison.
edited 30 Nov 2024 by tobias_maartens — added the method parameters
Aggregated, published test results and vendor ratings built from submitted batches. Methodology stated, dataset browsable, no listing fees.
Browse resultsThe honest answer is that most claimed differences between reputable suppliers are inside inter-laboratory noise.
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.
Put another way, 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.
Name the laboratory and the dates or the comparison cannot be reproduced.
Concretely, ratings on this site are ours alone and are deliberately not reconciled with anyone else's.
Cost per milligram of actual peptide is the honest price comparison, which means dividing by measured content rather than by label claim.
Sample size matters. One order each is an anecdote about six vials; three orders each over a year is the beginning of a comparison.
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.
Use a fixed documentation checklist rather than an impression.
More usefully, 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.
Compare content, not purity. Purity clusters and content does not.
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.
Publish the method with the result. A comparison without the laboratory named and the submission dates given is not reproducible by anyone.
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.
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.