How do I compare TFC and SSA on lead time to the United Kingdom?

Setup, so nobody has to ask: TFC · SSA · 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.

Mechanically, 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.

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.

This is the question where methodology matters more than the conclusion.

Sample size matters. One order each is an anecdote about six vials; three orders each over a year is the beginning of a comparison.

Publish the method with the result. A comparison without the laboratory named and the submission dates given is not reproducible by anyone.

Comparisons drawn from different laboratories at different times are weaker evidence than most people treat them as.

Use a fixed documentation checklist rather than an impression.

Start by asking what you are optimising for, because cost per milligram, documentation depth and lead time do not have a common winner.

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.

Mechanically, content is the more discriminating measurement than purity for supplier comparison, because purity clusters tightly among competent suppliers and content does not.

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.

edited 2 Jan 2026 by nadia_kowalczyk — updated for the 2026 guidance change

Concretely, 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.

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.

The caveat is that a comparison is a snapshot of the lots compared, and lots change.

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.

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

edited 4 Sept 2025 by ines_brandt — tightened the wording; no substantive change