How does UV-vis instrument ( double beam spectrometer)works?

Question

what happens when the sample beam blocked? when ref beam is blocked? If the sample or reference cuvet is dirty? what if we get negative absorption? can someone please help

Answer 1

The principle of a double beam spectrometer is that you can simultaneously measure the sample and reference cuvettes.

If you block the sample beam, the spectrometer will think that no light is coming through, resulting in ridiculously high absorbance.
If you block the reference beam, you will have a really high background, and the computer will try to subtract this from the sample reading. I think this is how you get a negative absorption reading.

Dirty cuvettes often lead to increased absorption, which results in either high absorbance, or low or negative absorption, as explained above.

Answer 2

They resolve components simultaneously.