Ultraviolet-Visible spectroscopy (UV/VIS) is the oldest form of spectroscopy. It uses light in the visible and adjacent near ultraviolet (UV) and near infrared (NIR) ranges. In this region of energy space molecules undergo electronic transitions. The method is used in a quantitative way to determine concentrations of absorbing species in solution, using the Beer-Lambert law:

A= ln(I/Io) = ε·c·l

A stands for the measured absorbance. Io for the incident intensity of the light at a given wavelength. I for the transmitted intensity. The length of the cell is represent by l and the concentration by c. For each species and wavelength ε is a constant known as the extinction coefficient.