Principles of UV/vis spectroscopy (4) Spectrophotometer configuration

July 9, 2020

Light source

A deuterium lamp (185 to 400 nm) is used for the ultraviolet region and a halogen lamp (350 to 3000 nm) is used for the visible / near infrared region. In some cases, a xenon flash lamp is also used. This kind of lamp is often employed together with a photodiode array (PDA) detector in HPLC.

Monochromator

The monochromator extracts light with a specific wavelength from a spectrum produced by a dispersion element such as a diffraction grating. The monochromator comprises an entrance slit, a collimator mirror, a diffraction grating, a condenser mirror, and an exit slit. Figure 10 shows the optical configuration of a typical Czerny-Turner type monochromator.

Fig. 10 Czerny-Turner monochromator

Cuvette

There are many types of commercially available cuvettes. These can be made from glass, quartz, or plastic, and can have optical path lengths from 5 to 100 mm. In addition to cuvettes with rectangular cross sections, shapes such as capillaries and flow cells are also available.

Detector

The detector in a UV/vis spectrophotometer is a transducer that converts light into an electrical signal. Typical examples include Si photodiodes (190 - 1100 nm) and photomultiplier tubes (PMT, 185 - 900 nm). PbS detectors (1000 - 3200 nm) and InGaAs detectors (1000 - 3200 nm) are used as near-infrared detectors.