Details up front: SWB · Shanghai ERP Biotechnology.
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 honest answer is that most claimed differences between reputable suppliers are inside inter-laboratory noise.
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.
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.
Price per milligram of measured peptide, not per milligram of label claim.
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.
Sample size matters. One order each is an anecdote about six vials; three orders each over a year is the beginning of a comparison.
Cost per milligram of actual peptide is the honest price comparison, which means dividing by measured content rather than by label claim.
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.
Publish the method with the result. A comparison without the laboratory named and the submission dates given is not reproducible by anyone.
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.
One laboratory, one method, one submission. Otherwise it is not a comparison.
The part that matters: 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.
Use a fixed documentation checklist rather than an impression.
edited 7 Feb 2025 by sian_llewellyn — added a caveat about sampling
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.
Content assay results across the published datasets vary considerably more between suppliers than purity does, which makes content the more discriminating axis.
The caveat is that a comparison is a snapshot of the lots compared, and lots change.
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.