Setup, so nobody has to ask: FGP · Xi’an Mokemei Biotechnology.
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.
Under what conditions does the answer flip?
This is the question where methodology matters more than the conclusion.
Lead time and lane behaviour are supplier properties too and are easier to compare than analytical ones, because they need no laboratory at all.
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.
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.
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 standardsThe short version: same compound, same laboratory, same method, ideally same week — otherwise you are comparing laboratories rather than suppliers.
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 is the more discriminating measurement than purity for supplier comparison, because purity clusters tightly among competent suppliers and content does not.
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.
edited 3 Aug 2024 by kwn_analytical — expanded the table to cover the lower concentration
Ratings on this site are ours alone and are deliberately not reconciled with anyone else's.
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, publish the method with the result. A comparison without the laboratory named and the submission dates given is not reproducible by anyone.
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.
Price per milligram of measured peptide, not per milligram of label claim.
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.
Cost per milligram of actual peptide is the honest price comparison, which means dividing by measured content rather than by label claim.
Content assay results across the published datasets vary considerably more between suppliers than purity does, which makes content the more discriminating axis.
One laboratory, one method, one submission. Otherwise it is not a comparison.
Start by asking what you are optimising for, because cost per milligram, documentation depth and lead time do not have a common winner.
Sample size matters. One order each is an anecdote about six vials; three orders each over a year is the beginning of a comparison.
Nothing here is medical advice, and research-use compounds are not approved for human use.
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.