What does a 97.9% purity with a batch certificate attached let me conclude?

Stated plainly: 97.9% · batch certificate.

I have read the primary source rather than the summary, which has left me with more questions.

I understand the headline. I do not understand the footnotes, and the footnotes look important.

What would I need in addition before this supported a decision?

Concretely, read the chromatogram before you read the number, because the number without the trace is not a measurement, it is a claim.

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.

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.

I would be careful about over-reading a single measurement — treat it as a data point, not as ground truth.

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

edited 23 Jul 2026 by dead_volume — expanded the table to cover the lower concentration

More usefully, understanding purity requires separating the chemistry from the method from the reporting convention, and the three are not independent.

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.

Mechanically, 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.