A colleague of mine who is new to our company tells me that from an FDA point of view that if you are assaying multiple actives in a pharmaceutical by LC, there cannot be a wavelength change for UV detection built into the method so that all actives can be assayed in the same method. She maintains that if such a wavelength change is required, then a separate method must be set up for that active. My position is that as long as the method has been validated and has, therefore been demonstrated to be suitable for its intended use, then such a wavelength change in the method is acceptable. Can someone give me some guidance on this?

I also work in a company that manufactures pharmaceutical products; I have never read or heard anything prohibiting a timed wavelength change. The FDA may not have 100% great logic, but I sure can't see a logical reason why they would find that unacceptable; in fact, USP/NF states acceptability as I quote from NF 621 dealing with HPLC detectors (USP 24, p. 1921): "Modern variable wavelength detectors can be programmed to change wavelength while an analysis is in progress". I agree with your position is that as long as the method has been validated and has, therefore been demonstrated to be suitable for its intended use, then such a wavelength change in the method is acceptable. If I had the chance to do two actives in one run using programmed wavelengths, I'd do that in a heartbeat; saving solvent (with less solvent disposal), materials, and operator time by combining into a single validated methodology should be commended.

I agree with Molever, it's better if you can control both wavelengths in the same run.

Another question is: If you don't have an external STD to control an impurity. Then you ave to control it at the same wavelength tan the main chromaotgraphic signal and then asume that the Rf (Response factors) are similar.

KAF

I would think this would be perfectly sound as long as this was not an impurities method.