The UV visible spectrometer measures the light’s absorption by a liquid sample, at a given wavelength between 200 nm and 800 nm. There are two different ways to use it:

• Measurement of absorbance A at a fixed wavelength; Beer-Lambert's law links this absorbance to the concentration of the solutes and several physical constants. This method is widely used for quantitative analysis, including in chromatographic detection, and is named spectrophotometry.
• Measurement of a given absorbance as a function of wavelength, on a sample at a specific concentration: the obtained graph is the UV-visible spectrum of the considered molecule in solution. It depends on its molecular structure.