Results (
Thai) 2:
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In simple cases Raman imaging can provide data on
API distribution within tablets in a very straightforward
fashion. For example, Fig. 4 shows a composite Raman
image comparing data from two tablets (half of each is
shown to highlight the differences) with the same overall
composition but different formulation protocols. These
pushbroom images were recorded at 100 lm micron spacing
on a 70/70 grid i.e. a total scan area 7 mm square to
allow the entire face of each tablet to be imaged. Accumulation
time was 5 s per point, leading to a total acquisition
time of approximately 7 h. Both tablets were prepared
from mefenamic acid (API) (20% by mass) with Lutrol binder
and lactose bulking agent. In one case the constituents
were prepared by normal co-melt fluidised bed granulation
i.e. the three constituents were granulated in a fluidised bed
whose temperature was taken above that of the melting
point of the binder. The solubility of this API in the Lutrol
binder is relatively low, which leads to non-uniform distribution
in the granules and ultimately the tablets prepared
from them, as shown in the Figure. The corresponding
image with higher uniformity of colour is one where the
API was first dissolved in binder and the resulting mass
reground before being granulated in a fluidised bed as
before. This procedure improves the uniformity of API distribution
in the granules and the tablets prepared from
them. There are numerous ways to treat these data, such
as plotting the relative band intensities of the API and binder/
excipient. However, in these images the data at each
pixel were compared to a standard (average) spectrum of
a sample which had API and binder/excipient band intensities
at the desired level by calculating a simple correlation
coefficient. In these images the positions where the correlation was high are white/pink while positions where there is
poorer correlation are green/blue. The spectra at the areas
showing blue are essentially pure API, as evidenced by
comparison of spectra obtained at these positions with that
of a pure API standard.
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