FRESH PERSPECTIVES
Figure 11 - Scores for PC 2 vs. PC 1 from PCA model of placebos with the addition of GLSW preprocessing (α = 0.1)
Figure 12 - Class predicted probability - PLSDA model with capsule placebos vs. all other classes
longer need to be included for analysis at the subsequent levels. This reduces the load during those steps by having to account for less sources of variability.
The fi rst step in constructing the hierarchical model is to classify each sample according to one of the following groups:
• • • •
capsule placebo from one of the original products tablet placebo from one of the original products
placebo from either NP1 or NP2 active
Next, the following PLSDA models were built (in the following order)2 Capsule placebos
:
Building upon the results in Figure 11, complete separation of the capsule placebos from all other classes – including the new products – proved to be successful with the addition of GLSW preprocessing (Figure 12)
Classes for modeling – capsule placebos (I); all other classes (II) Classes excluded: none
Tablet placebos
Excellent separation was achieved in classifying tablet placebos from the remaining samples (actives and placebos of NP1
and NP2
Figure 13. Classes for modeling – tablet placebos (I); actives, NP1
placebos (II) Classes excluded: capsule placebos
) as shown in placebos, and NP2 Placebos for NP1 and NP2
Having accounted for tablet and capsule placebos from the original products, the next step was to build a model that discriminated placebos from the new products against all actives. This model was somewhat less deterministic than the previous two, yet still useful. As can be seen in Figure 14, the discrimination between NP1 actives is successful with the exception of the NP2
/NP2
placebos and all of the active group. Hence, if an
2 Data over the spectral range of 201.7-1701.6 cm-1 was used for each model with the following preprocessing steps: 2nd derivative (15 pt. window, 2nd order polynomial), SNV, GLS weighting (α = 0.1), and mean centering
65 American Pharmaceutical Review | Fresh Perspectives 2013
Figure 13 - Class predicted probability - PLSDA model with tablet placebos vs. actives and placebos from new products
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