Chromatography Forum

I developed an LC method that satisfied our goal of identifying 2 compounds of interest. My dilemma is that at the same concentration, 1 compound absorbs UV 10 times as the other. What's the solution for this, and is it a problem in the first place? I'm using normal-phase LC.

Thanks lot.
Albert Roy

I do not think that this is a principle problem. However, you can try to find a wavelength where there is less of a discrepancy between both compounds.

What about a VWD detector where you could time-program a second wavelength or a multiple wavelength detector or DAD where you could simultaneously record multiple signals?

Thanks for the help. I'm going to transfer the method where the lab has no PDA detector, so use of other detectors beside single UV is not an option.

I would like to use time program, ie using different wavelength at certain time. for example, we have 2 substances with retention time 5 and 10 minutes (runtime 15 minutes). the max abs of substance A and B are 215 and 350 nm respectively. we could create a program that record the chromatograph as follow:
0 - 8 minutes: 215 nm
8 - 15 minutes: 350 nm

As long as both peaks satisfy the requirements for detection limit and linear range, there is no problem. There is a potential problem if the one wavelength is on a steep slope of the absorbance spectrum; it may be difficult to get good linearity and reproducibility.