Chromatography Forum

Good morning all,

I am working on a stability indicating method for which I am trying to find the response factor of one of the degradants (an unspecified degradant) that is almost at the qualification threshold assuming a 1:1 Response Factor. I wanted to know if there is a technique or an experiment that I could execute in order to determine more accurately the Response Factor of the degradant. I dont have a fraction collector to isolate the impurity. Any help is greatly appreciated. Have a good Monday!

MO

Any time you do not have a reference standard for an analyte, the response factor is nothing more than a guess. By assuming the same response factor for your degradant and the parent compound, you are making an educated guess, but it is a guess none the less.

That said, you could try using a detector whose response is (relatively) independent of analyte structure (e.g., the ELSD or CAD).

Hi

Close to the qualification threshold (0,15-1,0% depending on dose) you say. Tricky, I would recommend to determine the structure (ie get help with isolating it) as the identification threshold is same as qualification threshold apart for highest doses (id=0,10%) if recalling ICH Q3b right.

I assume you could also use a diode array detector and compare the unknown with the main peak and make a qualified guess about responsfactors. Potentially add some MS data to that

The potential issue I can see is potential regulatory questions if you do not build your case strong enough to exclude an identification of the unknown as you are so close to the qualification threshold.

I am aware that you can not feed us all info due to company policies, but things like: has this peak been present in clinical trials and if so at what level etc is also a factor to be considered.

Suppose the degradent has the same chromofore as the parent compound. It will have a similar spectrum, maybe shifted red or blue, but it could also have quite a different absorption coefficient. What looks like being at the limit could be maybe 10% of the parent. I am not using the word "active" here as the 10% degradent could be more active than the main compound. Its activity might be totaly different from the parent, it might be a killer. Are you going to guess that this possible degradent can be ignored? If you do, and get through with it, please state at least on the packaging slip that "This medication degrades to uncharacterized materials to an unknown extent. We guess that it can be ignored."

I am working on a stability indicating method for which I am trying to find the response factor of one of the degradants... I dont have a fraction collector to isolate the impurity.

What's wrong with injecting a larger quantity, and collecting the impurity peak manually ? - it's very easy...

Admittedly, it gets boring when you have to perform a 100+ injections. If the retention time is constant, you can even set up a little timer + low pressure valve to switch the desired fraction stream to a collection flask.

That way, you can confirm some relevant properties of the impurity, and you usually don't need much sample..

Bruce Hamilton