Figure 4From: Evaluation and differentiation of the Betulaceae birch bark species and their bioactive triterpene content using analytical FT-vibrational spectroscopy and GC-MSThe ATR-FT-IR spectra of the reference compounds, betulin, betulinic acid and lupeol in comparison with the absorbance of raw bark. The * symbol denotes the specific band of each reference compound that could be used for triterpenes differentiation.Back to article page