What I have: 99.4% · Janoshik · 97.1% · PeptideMeter.
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.
What does each option buy me, and what does it cost me?
Start from what the detector sees, because that tells you what the number means.
The fraction of your main peak that is actually your target versus isomers, fragments or related sequences is invisible without complementary identity testing.
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.
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.
The practical summary: ask for the chromatogram and the method, and ignore the headline number until you have both.
edited 13 Feb 2026 by e_dziedzic — expanded the table to cover the lower concentration
Analytical standards and reagents with traceable certificates. Every quantitative result you read inherits the accuracy of the standard behind it.
Shop standardsMore usefully, read the chromatogram before you read the number, because the number without the trace is not a measurement, it is a claim.
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.
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.
The caveat is that purity without identity is only half an answer — a high purity does not mean the peak is actually what you think it is.
If you are ranking vendors, specify a method and have all samples tested at the same place.
It helps to be literal here: 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.
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.
More usefully, mass on column affects detector linearity and peak overlap — overloading broadens peaks and hides neighbours, while underloading improves resolution but loses sensitivity.
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.
Compare purity within a single laboratory on the same method, never across laboratories.
More usefully, area percentage is not mass percentage, and conflating the two is the most common misreading of a purity figure.
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.
Worth noting that method standardisation is poor in the research-grade space compared to pharmaceutical work, so identical-looking methods can produce different results.
The practical summary: ask for the chromatogram and the method, and ignore the headline number until you have both.
The underlying point is that understanding purity requires separating the chemistry from the method from the reporting convention, and the three are not independent.
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 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.
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.