Is a 96.4% result from Janoshik comparable to 97.6% from Medutest?

Details up front: 96.4% · Janoshik · 97.6% · Medutest.

I want to know what the trade-off actually is rather than which option is fashionable.

I would rather have a defensible reason than a marginal improvement.

Which axes does this decision turn on?

96.4 and 97.6 are 1.2 percentage points apart, which sounds small until you restate it as impurity. Janoshik is leaving 3.6 per cent of the detected area unassigned and Medutest 2.4 per cent — a factor of 1.5 between them. The impurity fraction is the quantity that moves when a method changes, and it is the one worth arguing about; the headline is just its complement. Comparable means same column chemistry, same gradient slope, same detection wavelength, same integration convention. Until you have those four from both laboratories, 96.4 and 97.6 are two measurements of slightly different quantities that happen to share a unit.

Start from what the detector sees, because that tells you what the number means.

Retention time is sequence-specific and method-specific, so comparing your result to a supplier value using a different method is meaningless without method documentation.

Column pore size affects mass transfer — a 100 Angstrom packing on a 5 kDa peptide restricts diffusion, broadening the peak and potentially hiding small impurities in the shoulders.

Published side-by-side method comparisons show that a two-point difference in purity on the same vial is easily explained by method choice alone.

The practical summary: ask for the chromatogram and the method, and ignore the headline number until you have both.