Area percent versus weight percent: the confusion that causes most arguments — what changed since posts 31–35

This follows post #29 rather than contradicting it.

Before anything else: what was the gradient, and at what wavelength? Area percent at different wavelengths is not the same number even on the same sample because different species absorb differently at different wavelengths. With the method stated, I can tell you something useful. Without it, all I can say is that there is one large peak.

That is the shape of it. The detail is where I would expect to be corrected.

Area percent is a proportion of absorbance, not a proportion of mass. Two species with different extinction coefficients at the detection wavelength contribute unequally to the total, and nothing on the certificate corrects for that.

The general case is well covered; this is the awkward specific one.

Method validation is the demonstration that a method can separate the compound from its degradation products and impurities reliably. A method that cannot resolve an impurity from the parent peak will not detect that impurity.

I would rather post the uncertainty than round it away.

Before the thread moves on from Area percent versus weight percent — what is the sample size behind the claim? I am not being difficult; I have seen the same figure quoted from an n of four and from an n of four hundred.

For anyone finding this later: the short answer on Area percent versus weight percent is that it depends on one thing, and the rest of the thread is people identifying which thing.