X-RAY PHOTOELECTRON SPECTROSCOPY FOURIER TRANSFORM INFRARED

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					the atomization air pressure. Studies
using CLSM may facilitate a greater
understanding of the film formation
process and may also be used to investi-
gate the extent of drug migration into the
film at the interfacial region.

X-RAY PHOTOELECTRON
SPECTROSCOPY
Another technique recently used to inves-
tigate the film-tablet interfacial region is
x-ray photoelectron spectroscopy (XPS)
in conjunction with ion bombardment.
XPS alone has been used as an analytical
method to characterize solid surfaces in
both qualitative and quantitative terms.
XPS involves the application of mono-
chromatic x-rays to a solid sample, caus-
ing electrons from core orbitals of the
various atoms present to be ejected.
These electrons pass through an energy
analyzer and an electron detector. When
combined with ion bombardment, depth
profiling of the sample is achieved.
Similarly, laser induced breakdown spec-
troscopy (LIBS) is a depth profiling tech-
nique that uses laser pulses to bore into a
sample. Tableting excipients and coating
materials must possess unique atoms, ele-
ments, or functional groups in order to
use XPS or LIBS. These techniques are
currently being used to quantify the sur-
face dissolution of tablets that occurs
during the spray-atomization application
of a polymeric material and to evaluate
film thickness and coating uniformity.
Results from these studies will enhance
our understanding of the mechanisms
involved in film formation and polymer
adhesion. Furthermore, these analytical        FTIR (ATR-FTIR) may be used to investi-      ELECTRON PARAMAGNETIC
methods have the potential to explore the      gate solid surfaces, where the infrared      RESONANCE SPECTROSCOPY
migration of drugs and/or excipients into      light penetrates into the outer layers of    Electron paramagnetic resonance spec-
the film both during the coating process       the surface. ATR-FTIR is currently being     troscopy (EPR) is widely used to examine
and during storage.                            used to spatially characterize applied       free radicals in both chemical and biolog-
                                               polymeric films. Two-dimensional false-      ical processes. This technique has been
FOURIER TRANSFORM INFRARED                     color images based on signal intensities     modified to investigate the oxygen per-
SPECTROSCOPY                                   of IR frequencies of specific functional     meation kinetics through solid dosage
Fourier transform infrared spectroscopy        groups across the sample surface permit      forms and through applied polymeric
(FTIR) is a vibrational spectroscopic          chemical visualization of the film unifor-   films. This technique uses an oxygen-
technique used to gain information             mity. Current studies are investigating      sensitive lithium phthalocyanine crystal
regarding the chemical structure of a          the effects of processing parameters on      (LiPC) in the center of the drug product.
sample. Attenuated total reflectance           the uniformity of the film coating.          Individual dosage forms are placed in the



30   AAPS NEWSMAGAZINE        March 2003