2.2. The spraying nozzle height above the tissue sample
The position of the spraying nozzle above the sprayed sample is correlated with the intensity of obtained spectra, but the correlation depends on the matrix type. In the case of DHB, the peaks intensities are higher with the higher position of the nozzle (Z=5), but for norharmane, most intensive peaks are obtained at the lowest position (Z = 25). The same correlation is for 9AA (Z=5) and norharmane (Z=15) in the negative ionization mode. Sometimes, the visual effect of matrix application – such as local tissue damage or irregular crystallization – could be observed. Such circumstances determine the proper matrix application, as in the case of the NEDC matrix. Our study clearly shows that such basic optimization is necessary. For example, a higher nozzle height is frequently recommended for the lipid analysis, but unexpectedly for the norharmane lower position works better.