Chromatography Forum

Hi, everyone!
I have a question about some purity plots obtained from an active ingredient sample subjected to forced degradation.

When running the degraded samples under various conditions, I encountered two unusual purity plots: the first related to degradation under alkaline condition:
https://ibb.co/6YxsddT

The second under acidic condition:
https://ibb.co/Hg6GWwb

Are these plots acceptable, or should something be done?

Thanks in advance.

They seem weird, but I'm not too much into it.

But a threshold of 90° doesn't look right. Check the window where the purity blank is measured. Probably there's a peak or strong absorbing background?

The second peak is obviously a shoulder, so expect a non-purity result, due to the contribution of the main peak.
Also check the PDA manual for the theory of Empower's purity algorithm, and also Waters Knowledge-DB articles WKB46540, WKB85832

https://support.waters.com/Special:Sear ... &type=wiki

There is absolutely no possible way anyone could answer this question without YOUR complete method details AND all of the Peak Purity settings, reference peaks and parameters used in your software and method. Many of the settings (and esp the 'default' values, many of which are just place holders for real values) are subjective, so the results obtained can easily be adjusted to show almost any desired result. For them to have any value, the method must be optimized, the purity settings carefully manually adjusted with clean reference peaks and the parameters optimized.

Also, a threshold of 90% seems very low to use.

Agreeing w/ ^^^, you have some work to do still and the more you don't tell us, the more we can't help you.

It is unnecessary to do the spectral purity check (that is useless for related compounds with similar spectra) in order to see that the shouldered rider peak on the second image is very likely to consist of two or more unresolved peaks.