Page 85 - Tandem Techniques

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number of scans and adding them together and processing the sum. Such procedures improve the
resolution proportionally to the square root of the number accumulated scans. For example, 16
accumulated scans would increase the resolution by a factor of four. This, of course, is achieved at the
expense of time.

Figure 2.12
A Typical Interferogram
Courtesy of Nicolet Inc.

The accumulation of spectra also increases the sensitivity of the device, which is a useful advantage in
tandem systems, where the available sample from the chromatograph may be limited. Furthermore, as a
single scan may only take about a second to run, in order to double the sensitivity, the total scanning
time would only require to be increased to four seconds.

In general, tandem systems involving IR measurements have not been the most successful and, without
the introduction of the Fourier transform IR spectrometer, it is doubtful if IR tandem instruments would
have survived after the introduction of the faster and more efficient chromatography columns.

Raman Spectroscopy

If any substance, beitmay gaseous, liquid or even solid, is exposed to radiation of a defined frequency,
then the light scattered at right angles