Chromatography Forum

When running a degradant sample on the PDA Detector, can you put much store in the second derivative view? Example: I have a peak that could be my active but degrading or breaking down somehow *6 months 40 degree sample*. The UV spectrum of the peak is not like the usual active UV spectrum BUT when you look at the 2nd, 3rd and 4th derivative the lamba max value is there.

Does this suggest that the active peak is there somewhere but is just degrading? Some people have said that 2nd derivative means nothing and that if you don't get the distinctive uv spectrum shape from the 1st derivative you cant make any assumptions. Thoughts?

Not really. It's just a sales kimmick!

A degradant can degrade further like an ester to the organic acid and still have the same (almost) spectrum. But, in order to get a 100% verifiable identification (derivatization or not) you need ~100 mAU pure peak for comparison (at 1/2 height). So the peak height of the sample is very important and only good chromatography will solve this.