The use of these indicators is illustrated by a comparative study performed for the identification of the preprocessing function that is generating the most efficient PCA system screening for amphetamines based on their GC-FTIR spectra.
This result is explained by the correlation between the biological effect of amphetamines and the substitution pattern of the aromatic ring present in their molecular skeleton, the information about the latter structural feature being maintained by the GC-FTIR spectra.
The PCA training set consists of 30 GC-FTIR spectra, seven of which are the main illicit stimulant amphetamines.
The predictive power of the detection system may be improved by preprocessing the GC-FTIR spectra with various functions that may yield better defined clusters (see Figure 2).
In order to explain the results obtained with the GCQC and the associated analytical geometry indicators, each cluster has been analyzed by using the estimated density distribution of the PCA scores associated with GC-FTIR spectra.