How do I compare QST and MKM on lead time to the United Kingdom?

The particulars: QST · MKM · the United Kingdom.

These are treated as interchangeable and I do not think they are.

If both are acceptable I would like to know that, so I can stop thinking about it.

Under what conditions does the answer flip?

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.

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.

Stated carefully, publish the method with the result. A comparison without the laboratory named and the submission dates given is not reproducible by anyone.

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.

Name the laboratory and the dates or the comparison cannot be reproduced.

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.

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.

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.

Use a fixed documentation checklist rather than an impression.

edited 20 Jun 2025 by t_oyelaran — expanded the table to cover the lower concentration

Concretely, ratings on this site are ours alone and are deliberately not reconciled with anyone else's.

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.

Nothing here is medical advice, and research-use compounds are not approved for human use.

Price per milligram of measured peptide, not per milligram of label claim.

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.

Content assay results across the published datasets vary considerably more between suppliers than purity does, which makes content the more discriminating axis.

No supplier on this site pays for its position, and the storefront links are marked nofollow and sponsored.

One laboratory, one method, one submission. Otherwise it is not a comparison.

edited 20 Jul 2025 by marta_okonkwo — removed a claim I could not source