Attenuated Total Reflectance Absorption Spectroscopy
Absorption spectroscopy is a powerful technique used to identify and quantify a wide range of analytes since the absorption bands directly correlate to electronic or vibrational energy level transitions. Most molecular vibrations tend to have very low transition energies between 0.05 and 0.5eV, corresponding to wavelengths from 2.5 mm to 25 mm. While low energy, these vibrational transitions are incredibly narrow, providing a high degree of selectivity for material identification. On the other hand, electronic transitions are at much larger energies, typically >1.5eV, requiring visible or ultraviolet excitation. Unlike IR absorption bands, UV/ Vis absorption is far less discrete, making it less selective but more sensitive. For these reasons, the general rule of thumb is to use UV/Vis absorption for quantification and IR absorption for identification.