How do I read an impurity table on an orforglipron certificate against the 95.2% headline?

Accepted answer

Sum the table and see whether it reaches 4.8 per cent. A 95.2 per cent headline leaves 4.8 per cent of the detected area unaccounted for, and a related-substances table exists to say what that 4.8 per cent is. If the listed peaks add to 2.88 per cent, the missing 1.92 is unassigned area — real signal the laboratory saw and did not name — and that is a finding, not an omission. Check three things in order: does the table report each impurity as area per cent on the same basis as the headline; is there a reporting threshold below which peaks were discarded; and does the largest single impurity have a limit against it. A table whose entries do not close on 4.8 per cent is not wrong, but it is incomplete in a way the headline conceals.

In practice, 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.

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: gradient slope controls resolution, and gentler slopes resolve co-eluting impurities into separate peaks — so the better method reports the worse purity number.

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.