The wrapper
composition, particle size and crystallinity of powder drugs all affect their
NIR spectra. To remove these effects, one must apply proper spectral
preprocessing methods and good algorithms before developing a NIR quantitative
model.
Though different spectral
preprocessing methods possess different functions aimed at removing different
effects, we have found that use of the first
derivative+vector normalization (FD+VN) removes the effects of packaging bottle
and particle size in the NIR spectra.
The effect of
crystallinity cannot be removed with spectral preprocessing methods, but it can
be reduced by choosing a proper calibration set, choosing a specific principal
component, and applying partial least squares fitting.
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