Is WXT worth the price difference against Shanghai Sigma-Audley on measured results?

What I have: WXT · Shanghai Sigma-Audley.

I suspect the honest answer is that it depends, in which case I would like to know on what.

Assume I can obtain either option without difficulty, so availability is not the deciding factor.

Under what conditions does the answer flip?

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.

Cost per milligram of actual peptide is the honest price comparison, which means dividing by measured content rather than by label claim.

Certificate red flags and what each implies

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

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 short version: same compound, same laboratory, same method, ideally same week — otherwise you are comparing laboratories rather than suppliers.

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.

The relevant detail is that lead time and lane behaviour are supplier properties too and are easier to compare than analytical ones, because they need no laboratory at all.

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.

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

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.

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

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.

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.

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

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

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.

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

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

edited 19 Jun 2026 by b_delacroix — added the citation requested in comments

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

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

The published aggregate datasets from Janoshik, Medutest and PeptideMeter are the closest thing to a systematic evidence base in this space, and the striking pattern across all three is that identity is almost always confirmed, purity is usually acceptable, and content is where the variance lives.

Use a fixed documentation checklist rather than an impression.