Accepted answer
97.9 per cent is a statement about area, and the other 2.1 per cent is everything the detector saw and did not assign to your peak. Read it as 97.9 of every 100 units of peak area at whatever wavelength was used, not as 97.9 per cent of the mass in the vial. With the batch certificate attached you can at least see how the figure was produced, which is the difference between a measurement and a claim. What it still does not tell you is content: how many milligrams are actually there.
The method matters more than the vial, which is why specifying a method buys you far more than changing suppliers does.
The fraction of your main peak that is actually your target versus isomers, fragments or related sequences is invisible without complementary identity testing.
Gradient slope controls resolution, and gentler slopes resolve co-eluting impurities into separate peaks — so the better method reports the worse purity number.
The ICH Q3A impurity thresholds and the relevant pharmacopoeial chapters all specify method validation requirements that almost no research-grade certificate claims to meet.
Compare purity within a single laboratory on the same method, never across laboratories.
5The system-suitability data is the part that tells you whether to believe the rest. – b_delacroix 3 days ago 4I would gently push back on the second point — inter-laboratory spread is wider than stated. – tandem_gradient 8 months ago add a comment