Raman Chemical Imaging in conjunction with multivariate
statistical analysis enables the extraction of information
about the concentration and distribution of pure
compounds in a sample. A paper published in 2004 [55] elucidated
a multivariate approach to both global and local
Chemical Imaging and tested the proposed methodology
on Raman images of tablets. Five tablets, each with varying
amounts of API and excipient, were imaged using a
Raman point mapping system with 45 · 45 grid points
and 576 wavelengths between 8525 and 16420 nm. Global Principal Component Analysis (PCA) was applied to the
entire data set to determine the number of compounds
present. This was followed by local PCA, applied sequentially
to small subsets of the data, to examine the distribution
of compounds in the individual tablet samples. An
interative optimization approach was employed to minimise
model error.