RRF Determoination--Again

[gbalock]

I'm trying to determine if the genral practice of determining RRF's is done on a wt/wt basis or on a mole/mole basis. While this wouuld not pose a significant problem for normal dgradation products, where the difference in molecular weights between API and impurity are not significant, but where there is a significant difference in MW there would be a difference between the RRF's. With that said, what is your practice? FYI, we do our assays on a concentration basis.

[DR]

Assumption: You're working w/ UV detection.

To get an absolute RRF, one must know the extinction coefficient at a given wavelength of the deg. peak. This generally comes w/ knowing what the peak is, procuring a standard and determining its molar absorbtivity at said wavelength.

A RRF is really a comparison between the area counts (or height) per concentration unit of a deg. peak and that of the parent compound. It's just a ratio, meaning that whatever units you want to use for all of your peaks are up to you.