3. Concluding remarks
The followed approach (identification by HPLC-MS/MS and
subsequent imaging of substances) proved to be a suitable workflow
for the investigation of plant metabolite distributions in plant
organs. The initial HPLC-MS analyses are indeed reasonable, as
especially in case of flavonoids a high heterogeneity and
distribution is expected. Therefore, MS/MS measurements are
highly demanded, as without fragmentation no further assignment
to potential structures can be made. An identification of flavonoids
and other metabolites directly during MALDI measurements (e.g.
acquisition of survey spectra and fragmentation spectra of selected
abundant signals) might also be possible but could be hindered by
low abundance of analytes. Additionally, a decreasing intensity of
analyte signals would be expected by repeated MALDI measurements
from the same spot on the surface, due to consumption of
matrix. Nevertheless, by using highly focused laser beams and
performing MS/MS experiments around the locations, where survey
spectra originated from, a direct assignment of structures
would be possible without losing lateral information or sensitivity.
However, with the current setup and control of the AP-MALDI
interface no such patterns are possible. Nevertheless, the use of a
MALDI source that enables high lateral resolution (down to 3 mm)
proved to yield a detailed distribution of flavonoid diglycosides