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.
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