Would you accept 98.2% on cagrilintide from Homopeptide without a content assay?

Stated plainly: 98.2% · cagrilintide · Homopeptide.

I would like to set this up properly once, rather than adjust it repeatedly.

My budget is real but not tight, and my tolerance for uncertainty is low.

How would you structure this, and what thresholds would you set in advance?

98.2 per cent purity with no content figure leaves the milligram number unmeasured. Purity says 98.2 of every 100 units of detected area is cagrilintide and 1.8 is something else. Content says how many milligrams are in the glass. The two do not constrain each other: a vial can be 98.2 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 single most important distinction is between what purity measures — the fraction of detected material that is your target — and what you actually want to know — how much of the material in the vial is your target.

Temperature affects the dynamics of molecular conformation, and if a peptide has proline residues that interconvert on the chromatographic timescale, the peak will split or shoulder at low temperature and collapse at high temperature.

Put another way, 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.

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

edited 21 Jun 2026 by Dr_Ingrid_Baumgartner — expanded the table to cover the lower concentration

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.

To be exact about it, 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.

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.