Discussion
1. Different matrices, different pictures
Collecting such a great amount of analysis allows us to notice an
interesting observation: the obtained ion map of a particular ion could
differ dramatically regardless of the used matrix, the solvent
composition, or even the number of matrix layers.
In the positive ionization mode, we have observed this effect for the
norharmane and DAN matrices in comparison with the classical DHB matrix.
Norharmane produces a strong signal from lipids. Nevertheless, the
lipids seem to be located in a whole tissue area, and the discrimination
between the white and the gray matter is lost. For example, the ion map
for m/z 810 and 766 for the DHB matrix suggests that those substances
are present mainly in the white matter, but in the case of norharmane,
these peaks were present all over the tissue slice (see Fig. 18). This
effect occurs probably because the chloroform is used as a solvent.