Fig. 13 The relationship between the chosen peaks’ intensities
and signal-to-noise ratio (s/n) in terms of the number of matrix layers
(A) and the spraying nozzle height (B) for the negative ionization mode
rat spinal cord tissue slices (matrix: 6 mg/ml norharmane
(chloroform:MeOH:H2O))
Generally, for the negative ionization mode, norharmane gives the
spectra of higher intensity for the lipids around m/z = 728 compared to
9AA and then with the higher m/z range their intensities are going lower
(see: Fig. 21). Additionally, there is no signal observed for low m/z
ions like m/z = 255, or m/z = 283. It seems, that only the lipids of
higher molecular weights are able to ionize with this matrix.
N-(1-naphthyl) ethylenediamine dihydrochloride (NEDC) –
negative ionization mode
NEDC (7 mg/ml, 70% MeOH) is quite destructive when sprayed from the low
position of the spraying nozzle. This effect is seen in Fig. 14.
Spraying nozzle heights 25 and 15 gave quite intensive spectra, but the
problem with matrix crystallization could be clearly observed in the
picture. Therefore, spraying nozzle height at a value 5 seems
to be optimal. It gives quite good peak intensity for small molecules
and lipids and the s/n ratio is also acceptable (Fig. 15).