Linearity of unknown impurities

[centraing]

Hello,

Can somebody tell me how I can determine the linearity of an kwown (not commercialy available) or unknown impurities. The product must meet the requirement of <0.5% for kwown/unkwown impurities. I have two methods for determine the impurities:
- With an 0.5% reference soltution (comparison peak area major peak tot impurities peak).
- With an 100% product solution (0.5% area of the major peak).

Thank you,

[tom jupille]

If you do not have the impurities available, then you cannot "determine" the linearity. All you can do is to assume that the linear range you have confirmed for your major peak also applies to the impurities.

[krickos]

Hi

Well the original post is a bit unclear here, until further information I will assume that you talk about a total specification limit rather than a specific one.

For pharmaceuticals (see ICH Q2 and ICH Q3A-B +ICH Q6A guidelines for details) one can use the responsefactor of the product under certain events. See identification tresholds in named guidelines and ICH Q2 for validation information. Also other guidelines such as those surronding potential genotoxic impurities may apply depending on your case if you work with pharmaceuticals.

So might depend on the case and which industry standard you have to adhere to if you can use the product for linearity or if you have to identify it/isollate it or in worst case have it custom made after identification.