UV-Visible Spectroscopy : Principle; and Instrumentation, and application.

 UV-Visible Spectroscopy Principle:

• UV radiation : 200 nm to 400 nm, Or 10 nm to 400 nm.
• Near UV region : 200 nm to 400 nm
• Far UV region : Below 200 nm
• Visible radiation  region : 400 nm to 800 nm 
• Far UV is studied  under Vacuum condition.
• The common solvent preparing sample either ethyl alcohol Or Hexane.

Instrumentation:

      *Light Source

• Deuterium & hydrogen lams
• W filament lamp
• Xe arc lamp

      *. Sample containers

• cuvettes
• Plastic
• Glass
• Quartz    

1. The construction of a traditional UV- Vis spectrometer or very similar to IR, Similar functions, sample handling, irradiation, detection & output are required.
2. Here is a simple schematic that covers most modern UV spectrometers.
3. Two sources are required to scan the entire UV-Vis band:                                                                      Deuterium lamp: covers the UV 200nm - 330nm                                                                              Tungsten lamp: covers 330nm - 700nm.
4. The lamps illuminate the entire band of UV or Visible light;  the monochromatic (grating or prism) gradually changes the small bands of radiation sent to the bean splitter.
5. The beam splitter sends a separate band to a cell containing the sample solution and a reference solution.
6. The detector measures the difference between the transmitted light through the sample (I) VS the incident light (Io) and sends this information to the recorder. 
7. As with dispersive IR, time is required to cover, the entire UV-Vis band due to the mechanism of changing wave lengths.
8. A recent improvement is the diode-array spectrophotometer here a prism ( dispersion device) breaks apart the full spectrum transmitted through the sample.
   
9. Each band of UV is detected by a individual disades on a silicon wafer simultaneously- the obvious limitation in the size of the diodes, so some less of resolution over traditional instruments is observed.

Sample handling:

• Virtually all UV spectra are recorded solution phase.
• cells can be made of plastic, glass or quartz.
• Only quarty is transparent in the full 200nm - 700nm range; plastic and glass are only suitable for visible spectra.
• Concentration (We will cover shortly) is empirically determined a cyclical sample cell (commonly called a cuvel)
• Solvents must be transparent in the region to be observed; the wavelength where a solvent is no longer transprent is referred to an the cutoff.

 Practical Application of UV spectroscopy:

• UV was the first organic spectral method, however, it is rarely used as a primary method for structure determination.
• It is most used for combination of or with NMR & IR data to elucidate unique electronic features that may be ambiguous in there methods.
• It can be used to assay the proper irradiation wavelength for photochemical experiments or the design of UV resistant paints and coatings.
• The most ubiquitous use of UV is as a detection device for HPLC; since UV-Vis utilized for solution phase sample  vs. a reference solvents this is easily incorporated into LC design.