Question

What are the differences between UV absorbance and fluorescence spectroscopy?

Answer 1

One measures absorbance and the other fluorescence.

Explanation:

In UV absorbance you use light in the UV range (10 nm to 400 nm - I have never worked below 240 nm) and you measure how much light of a given wavelength passes through a solution (please see How does a spectrophotometer work? for more information).

In fluorescence spectroscopy you use a given wavelength of light to excite a molecule, and then monitor for fluorescence at a longer wavelength (note, the excitation and emission wavelengths are unique for the molecule).

One major difference between the two methods is the light detector in absorbance spectroscopy is in line with the light path and the sample, whereas in fluorescence spectroscopy the light source and detector are at `90^o` to each other, with respect to the sample.