Direct analysis of Stevia leaves for diterpene glycosides by desorption electrospray ionization mass spectrometry
The analysis of Stevia leaves has been demonstrated without any sample preparation using desorption
electrospray ionization (DESI) mass spectrometry. Direct rapid analysis was achieved using minimal
amounts of sample (0.15 cm 0.15 cm leaf fragment). Characteristic constituents of the Stevia plant
are observed in both the positive and negative ion modes including a series of diterpene ‘sweet’
glycosides. The presence of the glycosides was confirmed via tandem mass spectrometry analysis using
collision-induced dissociation and further supported by exact mass measurements using an LTQOrbitrap.
The analysis of both untreated and hexane-extracted dry leaves proved that DESI can be
successfully used to analyze untreated leaf fragments as identical profiles were obtained from both types
of samples. Characterization and semi-quantitative determination of the glycosides was achieved based
on the glycoside profile within the full mass spectrum. In addition, the presence of characteristic
glycosides in an all-natural commercial Stevia dietary supplement was confirmed. This study provides
an example of the application of DESI to direct screening of plant materials, in this case diterpene
glycosides.