Ultraviolet-visible
(UV-Vis) spectroscopy is a technique that identifies chemicals based on the
interaction of molecules with electromagnetic radiation in the
ultraviolet-visible region (10,000-33,333cm-1 or 300-1000
nm). Molecular absorbances of UV-Vis light cause electronic transitions within
molecules. These transitions typically occur with the presence of a transition
metal ion, or a conjugated organic molecule. There are UV-Vis reference
databases, but there is much less specificity in a UV-Vis spectrum compared to
MIR data, making it a secondary verification technique with unknown chemicals. Point analysis (“bench top”) systems are used for analyzing liquid phase
materials, although a few systems are also capable of analyzing gases and
solids. UV-Vis instrumentation has been scaled down to hand-held size for
specific colorimetric applications, but most research-grade instruments are of
larger size, and are often combined with NIR instrumentation. Instrument are
available that have either single light paths or multiple beams for
simultaneous analysis of reference samples.
Additionally, some instruments
are capable of making time-resolved measurements for kinetics experiments. UV-Vis is an extremely mature analytical
technique. Many instruments are
available commercially. Cost widely
variable and depends upon both the instrument configuration and the sophistication
of the data analysis software.