Page 115 - An Introduction to Analytical Atomic Spectrometry - L. Ebdon

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Figure 4.13
One optical arrangement in an echelle-based monochromator. In this case a Schmidt
cross-disperser is used to disperse the UV light instead of The prism which is used for visible
light only. This results in better transmission in the UV (reproduced with permission
from the Perkin Elmer Corporation).

sorter, resulting in a two-dimensional spectrum in which the blaze wavelength corresponding to each of
the different orders can be used.

Fourier transform spectrometers have been developed for the UV-visible region of the spectrum. Such
spectrometers make use of a Michelson interferometer. The principle advantages of such devices are
excellent resolution, the electronic recording of the whole spectrum and extremely fast scanning speed
(a few seconds). However, the main disadvantage of this technique stems from the fact that the whole
spectrum is collected. Extremely intense emission lines contribute to the noise in all regions of the
spectrum, thereby degrading the signal-to-noise ratio of less intense lines.

Other desirable features of a monochromator are stability and multi-element capability. Initially,
direct reading spectrometers, based on a polychromator, were used for simultaneous multi-element
analysis, although these were expensive, bulky and generally limited to specific elements. The
development of rapid-scanning monochromators under