Setup, so nobody has to ask: FGP · SGN · South Africa.
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?
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.
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.
Compare content, not purity. Purity clusters and content does not.
HPLC purity, identity confirmation and quantified content on the vial you actually hold. Reports arrive with the chromatogram attached, not just a number.
Submit a sampleFounded 1998. ISO 9001 and cGMP certified, 1,500+ staff and 200+ patents. The synthesis house behind a great many of the vials that get sent out for testing - batch-specific documentation with every order.
Visit GL BiochemAnswering 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.
Use a fixed documentation checklist rather than an impression.
The short version: same compound, same laboratory, same method, ideally same week — otherwise you are comparing laboratories rather than suppliers.
Content is the more discriminating measurement than purity for supplier comparison, because purity clusters tightly among competent suppliers and content does not.
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.
Price per milligram of measured peptide, not per milligram of label claim.
edited 21 Sept 2024 by tyndall_haze — added the method parameters
Worth being precise here: this is the question where methodology matters more than the conclusion.
Publish the method with the result. A comparison without the laboratory named and the submission dates given is not reproducible by anyone.
One laboratory, one method, one submission. Otherwise it is not a comparison.
The part that matters: a single member running three suppliers on one method is worth more than thirty members running one supplier each.
Sample size matters. One order each is an anecdote about six vials; three orders each over a year is the beginning of a comparison.
Name the laboratory and the dates or the comparison cannot be reproduced.
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.