RRF calculations

GOOD VALIDATION PRACTICE (cGVP)
1

Hi,

I want to calculate the RRF of my impurity by dividing the slopes of two linearity experiments: the slope of the linearity obtained for the impurity at low level level divided by the slope of the linearity of the API at the assay level. Is this right? all references say to divide the slopes at low level, why is that?

2

Low level is used because the slope of the linearity curve can be different than the assay (for instance).