Stability-indicating assays

[kvalliappan]

Hi all!

Will a stability indicating HPLC method developed using a UV detector (variable wave length) will be acceptable or is it mandatory to employ PDA detector, because of the peak purity aspect coming into picture. I find number of publications appear in reputed journals where UV-vis variable detector is only used.

I would appreciate if someone could clarify.

Thanks for your time.

[danko]

If you have the rationale for the assumption that all degradation products absorb light at the given wavelength, then I think it’s OK to utilize a single wavelength detector.
For instance, protein degradation is traditionally monitored at approx. 214 nm (peptide bonds absorption) and it’s commonly accepted.

Another assumption would be that the degradation products are all separated from the native compound. This would be documented under the specificity validation of the method.

Best Regards

[LC_labrat]

It depends on the type of assay. If it is for pharmaceuticals than I would recommend using a diode array detector. It will be difficult to show specificity without one. Degradants typically will have a similar lambda max and also spectrums. Your HPLC method may not be able to distinguish between them without verifying it using a spectrum. Especially when performing the stress testing. A DAD detector is very useful when unknown peaks arise in stability studies.

[danko]

Degradants typically will have a similar lambda max and also spectrums

That’s exactly the situation in which a PDA detector would be as useful as a single wavelength detector.

Besides, I didn’t suggest any particular detection mode for the specificity study/documentation. PDA and/or MS detection would be the preferred detection techniques under development of the method, but ones the specificity (especially regarding degradation) and the quantitation issues are clarified then a single wavelength detection is often adequate.

Best Regards

[LC_labrat]

Will a stability indicating HPLC method developed using a UV detector (variable wave length) will be acceptable or is it mandatory to employ PDA detector, because of the peak purity aspect coming into picture.

A UV detector will not show co-eluting peaks so a PDA is needed to verify peak purity in stability indicating methods.

[Alex Buske]

To labrat:
A PDA can detect a coeluting impurity with a different UV-Spectrum; it is, however, useless when API and degradation product share the same chromophore.
So the Phrase "the peak is pure, because it passed purity testing (or has a peak purity value of 0.898 )" is certainly wrong. The only thing one could say is : The peak is impure because it didn't pass peak purity.

Alex

[LC_labrat]

Certainly there is more to a peak purity, a PDA is not conclusive, as with any technique it has limitations.