percent impurity calculation (HPLC)

[jayroseville58]

Just wondering, what is the difference of calculating percent impurity by basing individual peak area over total peak area and by basing the individual peak area over main peak area?

What is the right way of calculating percent impurity on HPLC instead? Thanks.

[danko]

The total – of course!

Just do a mental experiment: Your sample is degraded such as a degradation peak of interest has 10,000 AU the main peak has shrunken to 10,000 AU as a result of the degradation.
Now do the math, comparing to the main peak and tell me what you think

Best Regrds

[jayroseville58]

The total – of course!

Just do a mental experiment: Your sample is degraded such as a degradation peak of interest has 10,000 AU the main peak has shrunken to 10,000 AU as a result of the degradation.
Now do the math, comparing to the main peak and tell me what you think

Best Regrds

thanks for the reply,
can you explain it further. Please.

[danko]

Just divide these 2 areas and multiply by 100.
So you get 100% degradation peak. That isn't right - is it?

Ok?

Best regards

[jayroseville58]

Just divide these 2 areas and multiply by 100.
So you get 100% degradation peak. That isn't right - is it?

Ok?

Best regards

Yes for me also I think that is right, but how come other references especially some other Licensor's reference was using peak area of the impurity over peak area of the main peak?

[danko]

Believe me I've seen many irrationale procedures arround in the course of time.
I can write a book if I compile them one day

Best regards

[jayroseville58]

Believe me I've seen many irrationale procedures arround in the course of time.
I can write a book if I compile them one day

Best regards

Here is another thing. When You say total peak area, does it include the peak area of your mobile phase, placebo and diluent? Thanks.

[danko]

Only relevant peaks of course – i.e. the main peak + all other degradation peaks originating from the substance.
You should think of it like this: Percentage of what? My drug substance or everything detectable And keep in mind that all degradation peaks originate from the substance and for that reason should be included. Mobile phase, placebo and diluent peaks should be excluded.

Best Regards

[jayroseville58]

Only relevant peaks of course – i.e. the main peak + all other degradation peaks originating from the substance.
You should think of it like this: Percentage of what? My drug substance or everything detectable And keep in mind that all degradation peaks originate from the substance and for that reason should be included. Mobile phase, placebo and diluent peaks should be excluded.

Best Regards

Thanks

[gtma]

I think %a/a approach becomes tricky when some of the impurities have significant RRF. I believe the %a/a becomes meaningless and %w/w should be reported. For %a/a, do u correct the impurities in the demominator for RRF and then later correct the numerator for RRF to convert to %w/w for each impurity? I'm assuming the impurities peak areas/RRFs are significant to affect the total area.