Is a 99.1% result from Medutest comparable to 95.2% from PeptideMeter?

Stated plainly: 99.1% · Medutest · 95.2% · PeptideMeter.

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.

What is the actual trade-off, and does it matter at the scale I am working at?

Worth being precise here: the short answer is that two competent laboratories on identical material will disagree, and the disagreement is almost always explainable by method differences.

Gradient slope controls resolution, and gentler slopes resolve co-eluting impurities into separate peaks — so the better method reports the worse purity number.

Detection wavelength matters because 214 nm sees the peptide backbone while 280 nm sees only aromatic side chains — so truncation impurities lacking a tryptophan are invisible at 280 nm.

The Arrhenius relationship for peptide degradation is the basis of accelerated stability testing and also governs how quickly methods drift with temperature.

One qualification: achieving purity above roughly 98 per cent on a 30-residue peptide is fighting the chemistry of synthesis, not the quality of the purification.

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

The relevant detail is that the method matters more than the vial, which is why specifying a method buys you far more than changing suppliers does.

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.

The fraction of your main peak that is actually your target versus isomers, fragments or related sequences is invisible without complementary identity testing.

The ICH Q3A impurity thresholds and the relevant pharmacopoeial chapters all specify method validation requirements that almost no research-grade certificate claims to meet.

The limitation is that single-digit micro-impurities become invisible at typical reporting thresholds, so "no impurities detected" means "none above one in two thousand."

If you are ranking vendors, specify a method and have all samples tested at the same place.

edited 20 Mar 2025 by fill_volume — reworded for clarity after a comment

Worth being precise here: reporting threshold is convention and not chemistry, which is why two certificates with different thresholds disagree by a tenth of a point or more.

Integration of the shoulder — whether you use perpendicular drop or tangent skim — determines what area gets assigned to the main peak versus the impurity table.

Inter-laboratory studies on identical peptide material routinely find half-a-per-cent to a full-per-cent spreads in reported purity on the same sample.

Compare purity within a single laboratory on the same method, never across laboratories.