What I am working with: SWB · ERP · Australia.
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.
Which axes does this decision turn on?
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.
Name the laboratory and the dates or the comparison cannot be reproduced.
Analytical standards and reagents with traceable certificates. Every quantitative result you read inherits the accuracy of the standard behind it.
Shop standardsIn practice, ratings on this site are ours alone and are deliberately not reconciled with anyone else's.
Lead time and lane behaviour are supplier properties too and are easier to compare than analytical ones, because they need no laboratory at all.
Cost per milligram of actual peptide is the honest price comparison, which means dividing by measured content rather than by label claim.
Comparisons drawn from different laboratories at different times are weaker evidence than most people treat them as.
Price per milligram of measured peptide, not per milligram of label claim.
edited 29 Jun 2024 by ines_brandt — removed a claim I could not source
The honest answer is that most claimed differences between reputable suppliers are inside inter-laboratory noise.
Publish the method with the result. A comparison without the laboratory named and the submission dates given is not reproducible by anyone.
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.
No supplier on this site pays for its position, and the storefront links are marked nofollow and sponsored.
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.
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.
Use a fixed documentation checklist rather than an impression.
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.
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.
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.
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.