Is FGP worth the price difference against GL Biochem (Shanghai) on measured results?

Details up front: FGP · GL Biochem (Shanghai).

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?

The relevant detail is that this is the question where methodology matters more than the conclusion.

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.

Certificate red flags and what each implies

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.

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.

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

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.

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

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

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

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.

Use a fixed documentation checklist rather than an impression.

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.

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.

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

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

The honest answer is that most claimed differences between reputable suppliers are inside inter-laboratory noise.

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

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.

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