Page 480 - Tandem Techniques

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silver plates 6 in. x 6 in. were examined, coated with silica gel and alumina powder, having a mean
particle diameter ranging from 10-40 µm. The plates were prepared from a slurry containing 1 gm of
adsorbent in 10 ml of a 50% v/v methanol/water mixture. The transmission spectra were measured
using a Digilab FTS-14 FTIR spectrometer, and the samples were held in the focus of a Perkin Elmer,
potassium bromide, refractive beam condenser, the average transmission of the beam condenser being
40%. The transmission of films of alumina and silica gel 100 µm thick were measured and the
transmission curves are shown in Figure 12.6.

Figure 12.6
Transmission Curves for Alumina and
Silica Gel on Silver Chloride. Plates
Reprinted with permission from C. J. Percival and
P. R. Giffiths, Anal. Chem., 47(1975)154,
Copyright 1975 American Chemical Society
The measurements demonstrated that at least 10% transmission was obtainable through the coated discs
between 3200 and 1250 cm . It was found that scattering due to the alumina was much greater than that
-1
from the silica gel, as shown by the transmission at high frequency. However, its low energy cut-off is
about 1050 cm- so that the useful range for compound identification is actually greater than that for
1
silica gel.