Would you accept 99.1% on orforglipron from QYB without a content assay?

Details up front: 99.1% · orforglipron · QYB.

I would rather over-plan the first cycle and simplify later.

I am prepared to do the work if someone can tell me which work matters.

What does a sensible plan look like, and what are the decision points?

On the detail: start from what the detector sees, because that tells you what the number means.

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.

It helps to be literal here: 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.

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

Compare purity within a single laboratory on the same method, never across laboratories.

edited 20 Jan 2026 by ekaterina_volk — tightened the wording; no substantive change

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

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.

Mass on column affects detector linearity and peak overlap — overloading broadens peaks and hides neighbours, while underloading improves resolution but loses sensitivity.

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.

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.

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.

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 practical summary: ask for the chromatogram and the method, and ignore the headline number until you have both.

The honest answer is that the achievable range of plausible purity figures for a given vial is wider than most people expect.

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.

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.