For reference: 97.1% · survodutide.
I would rather understand the derivation than memorise the outcome.
Two people I asked gave two answers that differ by a factor of ten, which is suggestive.
Can someone show the working rather than just the answer?
The underlying point is that purity is a method-dependent figure, and that is not a limitation of the measurement, it is a property of what the measurement actually answers.
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.
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.
I would be careful about over-reading a single measurement — treat it as a data point, not as ground truth.
The practical summary: ask for the chromatogram and the method, and ignore the headline number until you have both.
edited 28 Sept 2024 by birk_nordahl — added a caveat about sampling
Aggregated, published test results and vendor ratings built from submitted batches. Methodology stated, dataset browsable, no listing fees.
Browse resultsThe relevant detail is that start from what the detector sees, because that tells you what the number means.
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.
Sample solvent strength affects peak shape — if you inject in strong solvent on a gradient starting in weak solvent, the solvent peak can distort your main peak or create a false shoulder.
Proline conformer interconversion kinetics are well-characterised and the half-life is of the same order as the chromatographic peak width at room temperature.
If you are ranking vendors, specify a method and have all samples tested at the same place.
Worth being precise here: identity and purity are orthogonal, and a high purity says almost nothing about whether the peak is actually what you think it is.
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.
In practice, the fraction of your main peak that is actually your target versus isomers, fragments or related sequences is invisible without complementary identity testing.
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.
Compare purity within a single laboratory on the same method, never across laboratories.
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.
Buffer versus acid in the mobile phase changes the ionisation state of basic and acidic residues, shifting retention and selectivity — same vial, potentially different separation.
The practical summary: ask for the chromatogram and the method, and ignore the headline number until you have both.
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.
Mass on column affects detector linearity and peak overlap — overloading broadens peaks and hides neighbours, while underloading improves resolution but loses sensitivity.
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.
If you are ranking vendors, specify a method and have all samples tested at the same place.
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.