Compounds with varying UV absorbance

[Albert Roy J]

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

[Uwe Neue]

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.

[Consumer Products Guy]

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?

[Albert Roy J]

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.

[syx]

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

[Mark Tracy]

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.