Chromatography Forum

Hi All,

I was wondering about how to justify a normalisation procedure for related substance to the regulatories.

When I inject a sample solution, I use a 1% solution to calculate the%unknown related substance relative to the main peak in the 1% reference.
But if I look at the %area it's equal to the calculated %.
So I was thinking that normalisation can be used, and is even more precise because it's not influenced by weighing errors.
But how do I justify this approach in my report to the regulatories?

Any ideas?

Thanks for your time

Ace

You have to demonstrate that you have the requisite 3+ orders of magnitude linear range (i.e., all the peaks are in the linear range of the method). That begs the question of any assay of this type: the assumption that all peaks have the same molar absorbance.

Hi Tom,

the linearity isn't a problem, I already tested it from 0.01% to 130%..... for my main component. But I also have some small peaks, for which it is accepted to use a 1% reference by the pharmaceutical regulatories.
But I can't purify all of them and determine their molecular absorbance.
Or is there another way?

Ace