Analytical Chemistry

Table 9.1 Components of instruments used for ultraviolet, visible, infrared and magnetic resonance spectrometry.

Spectrometric

technique Energy source Cell material Monochromator Detector

ultraviolet hydrogen or

deuterium lamp

quartz

phototube, photomultiplier

or diode array

visible tungsten-halogen lamp glass

infrared heated ceramic alkali halide or

water-resistant

material glass

thermal or photon

magnetic resonance RF transmitter glass RH receiver

each of which receives a narrow band (2–10 nm wide) of radiation from the monochromator through the
UV or the UV and visible regions. This facilitates the continuous monitoring of a wide spectral range
and, using computer control, the recording, storage and display of a spectrum on a VDU screen in about
0.1 second. This type of instrument has found particular use as an HPLC detector. Cheap, simple
instruments for quantitative work in the visible region use coloured filters with a relatively wide
bandpass. These are variously known as filter-photometers, absorptiometers or colorimeters. Infrared
instruments are now predominantly of the Fourier transform type employing an interferometer (Figure
9.2(b) and p. 280), the cheaper and simpler dispersive spectrophotometers having declined in popularity.
Most ultraviolet, visible and infrared instruments now benefit from microprocessor or microcomputer
control, many displaying recorded spectra on a VDU screen. The software available with these
instruments for spectral manipulation, storage and library searches is becoming increasingly
sophisticated (p. 525 et seq.).

Quantitative Analysis

Quantitative methods based on the absorption of electromagnetic radiation involve measurement of the
reduction in intensity of the radiation on passage through an absorbing medium, i.e. the sample. The
degree of absorption is determined by comparing the intensity of the transmitted beam when no
absorbing species is present, i.e. a blank, with that transmitted by the sample. For monochromatic,
collimated radiation passing through a homogeneous liquid sample, the reduction in intensity of the