FIGURE 7.9 Electropherogram of E. angustifolia and E. pallida root (a) and E. purpurea and E. pallida root (b) mixtures. The arrows evidence peaks specific to E. angustifolia (an), E. pallida (pal), or E. purpurea (pur). Peaks: echinacoside (1), 6-O-caffeoyl-echinacoside (3), chlorogenic acid (5), isochlorogenic acid (6), cynarine (7), caffeic acid (8), isochlorogenic acid II (9), 2-caffeoyl-tartaric acid (10), and cichoric acid (11). (From Pietta, P.G. et al., 1998, Planta Med., 64: 649-652. With permission.)
a particular component, that is, isomers that provide identical spectra. The use of authentic standards for comparing elution times and spectra is required for unequivocal structural identification.
Among the different ionization techniques, the electrospray (ESI) and thermospray ionization (TSP) mass spectrometry appear particularly well suited, since these involve soft ionization that produces in most cases only protonated molecular ions [M + H]+ without fragmentation.
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