Figure 3
Statistical analysis performed on µATR-FTIR spectra for the 3770–2750 cm−1 interval. The hierarchical relationship between the spectra is represented by the dendrogram depicted in (a), while (b, c) show the estimation of the number of clusters using the average silhouette width and the obtained silhouette of clusters, respectively. PCA results, µATR-FTIR spectra, and the most representative (i.e., deepest) curve for each identified cluster (highlighted with different colours) are illustrated in (d–f). For clarity, the most external spectra of the clusters are underlined in (d) with the grey colour.
