Effects of normalization on feature selection in pyrolysis gas chromatography of coal tar pitches

Computerized calculation of variance weights sometimes detected important features that were not obvious from visual inspections of chromatograms for any two of three classes of coal tar pitches. In addition, normalizations by one or more peak areas or of peak heights, procedures often resorted to as a means of minimizing the effect of differences in size or sample heterogeneity, generally resulted in decreasing the weights of all features. Finally, a successful means was devised for correcting the chromatograms obtained using a column that had gradually degraded during a long series of runs.