Page 90 - Tandem Techniques

Page 71

the unprepared tablets themselves, the spectra differ considerably, as shown in Figure 2.16.

Figure 2.16
IR Diffuse Reflectance and Raman
Spectra of an Aspirin Tablet
Courtesy of the Perkin Elmer Corporation

It is seen that the situation has now quite changed, the infrared spectrum is virtually useless whereas the
Raman spectrum remains similar to that obtained from the powder. One of the great advantages of
Raman spectroscopy is that it is virtually independent of the form that the sample takes. This could be a
benefit that should be taken into account when a tandem system incorporating the Raman spectrometer
is being considered.

Unfortunately, the technique is even less sensitive than IR spectroscopy so its value as an identifying
technique in a tandem system appears to be rather limited. Nevertheless, the use of a laser light source
in conjunction with FT/IR will help in this respect, particularly if employed with the LC/IR interfaces
presently available. Such a combination might render an LC/Raman tandem system quite practical and
such possibilities will be discussed when dealing with LC/IR interfaces.