Setup, so nobody has to ask: 97.6% · a GLP-1 receptor agonist · HJ.
I am trying to build something sustainable rather than something thorough that I will abandon.
I have already decided the broad direction; this is about the specifics.
What should I decide now, and what should I defer?
97.6 per cent purity with no content figure leaves the milligram number unmeasured. Purity says 97.6 of every 100 units of detected area is a GLP-1 receptor agonist and 2.4 is something else. Content says how many milligrams are in the glass. The two do not constrain each other: a vial can be 97.6 per cent pure and still be under label, because water and counter-ion are part of the gross mass and neither shows up as an impurity peak. If you buy one test, buy the one that changes your arithmetic.
The part that matters: gradient slope is the most powerful parameter and almost nobody mentions it, which is why two reports on the same material disagree by a point.
Tailing factor measures peak shape, and a badly tailing peak spreads into the region where small impurities live, forcing tangent-skim integration that assigns tail area to the main peak.
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.
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.
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.
If you are ranking vendors, specify a method and have all samples tested at the same place.
Aggregated, published test results and vendor ratings built from submitted batches. Methodology stated, dataset browsable, no listing fees.
Browse resultsThe short answer is that two competent laboratories on identical material will disagree, and the disagreement is almost always explainable by method differences.
The fraction of your main peak that is actually your target versus isomers, fragments or related sequences is invisible without complementary identity testing.
Stated carefully, mobile phase additive choice affects ionisation and peak shape — TFA gives sharp peaks but suppresses mass spectrometry signal, formic acid gives worse peaks but preserves signal.
The practical summary: ask for the chromatogram and the method, and ignore the headline number until you have both.
Ask PeptideStack is a static archive. Posting is closed, but the norms are worth stating: answer the question that was asked, show your working, cite the trial or the certificate, and say plainly where the evidence runs out.