Fig. 11 The reduced quality of the ion map with increasing number of matrix layers without and with normalization (TIC – total ion current and RMS - root mean squared) – negative ionization mode (9AA 7 mg/ml 70% EtOH).
Norharmane (6 mg/ml matrix (chloroform:MeOH:H2O)) – negative ionization mode
In the case of norharmane (6 mg/ml in chloroform:MeOH:H2O, 1:1:1, v/v/v solution) the intensity of the peaks on the spectrum increased with the number of the matrix layers but starting from the 12 layers, further increase was minor. Conversely, the s/n ratio decreases starting from the twelfth layer. Thus, up to 12 matrix layers seem to be optimal. For the spraying nozzle position, 15 mm is performing the best since the intensity, and s/n ratio is relatively high. Lower nozzle position does not change the intensity but might be responsible for the molecule’s delocalization (see: Fig 12, 13).