Figure 2.

(a) Score plot resulting from the PCA of the IR spectra of the [M+Cs]⁺ (blue), [M+Li]⁺ (red), [M+Na]⁺ (green), [M+NH₄]⁺ (light blue), [M+Cl]⁻ (orange), and [M–H]⁻ (purple) ions of d-glucose (circles), d-mannose (stars) and d-galactose (squares). A smaller distance between two points correlates with greater similarity between two spectra. (b) Normalized surface areas enveloped by the triangles drawn in (a), which are a measure for the degree of variation in each set of hexose spectra.