Hi All,

I apppreciate your input on this one. In HPLC method validation for impurities (~0.1% WRT API), is it a must to use the API for the calibration curve (for the quantification of the impurity or impurities). This is going to be a problem if my impurity and API have different extinction coefficients at a particular wavelength (eg at 214nm, 0.1ug of my API and impurity have slightly different absorbances and at higher concentration this difference is greater so two curves have differnt slopes). In that case, what is the most appropriate quantification method? Should I use the impurity for the calibration curve or the API? or any other way of doing it? By the way this is a problem I encountered in a method validation.

Thanks in advance.

Ananda S.

sorry for the wrong title (I typed a new one but didnt replace the old one)
Ananda

I would construct two curves. I would use an impurity standard for an impurity level curve and the API reference standard for an assay level curve.

Actually we have another RP-HPLC method for the API and this particular method is validated only for the impurity. In this case I also prefer to use the impurity for the calibration not the API but one of my colleagues confused me.

Thanks Tom!

Ananda