Chemistry Reference
In-Depth Information
Several possibilities exist to enhance the sensitivity of Raman spectroscopy. For example,
use of ultraviolet (UV) laser irradiation at wavelengths of, for example, 266 nm allows for
signi
cant enhancements in sensitivity for typical drug molecules both by resonance
Raman enhancement and under normal Raman scattering [86]. The availability of reso-
nance Raman enhancements obtained by use of a 266 nm laser allows for signi
cant signal
enhancements for the drug di
unisal when present at 1% (w/w) in an amorphous dispersion
in PVP, as shown in Figure 4.6. The corresponding FT Raman spectra obtained using a
1064 nm laser, also shown in Figure 4.6, exhibit the low signal intensity for di
unisal that
would normally be associated with drug at this level. This approach allows for more
1% diflunisal in PVP
FT Raman, 1064 nm
PVP
FT Raman, 1064 nm
1% diflunisal in PVP
UV Raman, 266 nm
PVP
UV Raman, 266 nm
Diflunisal Form I
UV Raman, 266 nm
Diflunisal Form I
FT Raman, 1064 nm
1600
1400
1200
Raman shift (cm
-1
)
1000
800
600
400
Figure 4.6.
Spectra obtained by confocal UV Raman microscopy analysis of a 1% (w/w)
dispersion of di
unisal in PVP [86]. The UV Raman spectrumof the dispersion was obtained using
266 nm laser irradiation, 25mW laser power, a 20× objective, and 32 s acquisition time, andwas a
single point taken from a 22 × 22 map that required 4 h. The FT Raman spectrum was obtained
using conventional backscattering detection on bulk powder, 1064 nm laser irradiation, 400mW
laser power, and 18min acquisition time. Similarly obtained spectra of crystalline di
unisal
Form I are also shown for comparison. Resonance Raman enhancement is observed for the band
at 1612 cm
1
in di
unisal. FT Raman spectra were obtained using a Bruker Optics MultiRAM
spectrometer equipped with a 1064 nm laser and using 400mW of laser power, 4 cm
1
resolution, and 512 accumulated scans.
