eBook: Raman Imaging in Pharmaceutical Research - 12

Identifying Microparticles with
Raman Imaging
Miriam Böhmler, Wolfram Ibach, Keiichi Nakamoto, Damon Strom, and Eleni Kallis
These investigations illustrate the utility of the
ParticleScout software tool and confocal Raman microscopy
for microparticle analyses in the fields of
pharmaceutics and cosmetics.
Microparticles can be found everywhere, from pigments
in paint and titanium dioxide in sunscreen to
microplastics in water. In pharmaceutical and cosmetic
products, microspheres and microcapsules
often serve as carrier systems for drugs or bioactive
substances. The sizes or shapes of these particles
can severely influence the pharmacokinetics of the
contained active ingredient.1
Qualitative and quantitative
microparticle analyses are thus of growing interest
for research, development and quality control
in the pharmaceutical and cosmetics industries.
Raman microscopy is widely applied in pharmaceutical
studies, including particle investigations, as it is
a non-destructive and label-free technique for the
chemical identification of substance.2,3
In combination
with particle analysis algorithms, it is well-suited
to addressing the challenges of microparticle
studies, such as automating the procedures for finding
even the smallest particles (< 1 µm) and characterizing
them according to chemical and structural
properties.4
WITec alpha300 Raman microscopes
equipped with ParticleScout provide the sensitivity,
resolution and speed required for quick and comprehensive
microparticle analyses.
Particle analysis workflow
Particle analysis typically begins with a white-light
image overview. The challenges of generating a
large-area image at high resolution and contrast
are met by the combination of image stitching
and focus stacking. Image stitching records several
high-resolution pictures of adjacent areas and combines
them into one image. Focus stacking acquires
several pictures from different planes along the z-axis,
resulting in all the particles having sharp outlines
irrespective of their size and shape. In the obtained
overview image, ParticleScout then locates the particles
by a user-defined brightness threshold, which
makes finding particles fast, easy and reproducible.
Structural properties, such as perimeter, aspect ratio
or circular equivalent diameter, are then calculated
for each particle and can be used for classification.
ParticleScout then automatically records the
Raman spectra of all particles of interest. For chemical
identification of the sample components, WITec's
TrueMatch Raman database management software
is seamlessly integrated with ParticleScout. Thus, a
material can be assigned to each particle, making
it possible to correlate chemical and physical properties
and generate detailed reports that reveal the
sample composition.
12
eBook: Raman Imaging in Pharmaceutical Research

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