Matrix-assisted laser
desorption/ionization imaging mass spectrometry
(MALDI IMS) can determine the chemical identity and spatial distribution
of several molecules in a single analysis, conserving its natural
histology. However, there are no specific studies on the spatial distribution
of alkaloids in Erythroxylum coca leaves by MALDI
IMS, preserving the histology of the monitored compounds. Therefore,
in this work, positive-ion mode MALDI Fourier-transform ion cyclotron
resonance imaging mass spectrometry (MALDI(+)FT–ICR IMS) was
applied to identify and analyze the distribution of alkaloids on the
surface of coca leaves, evaluating the ionization efficiency of three
matrices (α-cyano-4-hydroxycinnamic acid (CHCA), 2-mercaptobenzothiazole
(MBT), and 2,5-dihydroxybenzoic acid (DHB)). The last was chosen as
the best matrix in this study, and it was studied in five concentrations
(0.5, 1.0, 2.0, 4.0, and 8.0 mg·mL–1), where
2 mg·mL–1 was the most efficient. The washing
of coca leaves with the organic solvents (acetonitrile, methanol,
toluene, and dichloromethane) tested did not improve the performance
of the ionization process. Finally, a tissue section, 50 μm
thick, was used to study the inner part of the leaf tissue, where
alkaloids and flavonoid molecules were detected.
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