Fig. 15 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: 7 mg/ml NEDC (70% MeOH) – (m/z 215 – [glucose +Cl-]).
NEDC is the only matrix able to decrease peaks intensities with the increasing number of the matrix layers, which is observed for low MW compounds that could be observed with this matrix (see: m/z 215 for glucose and 174 for glucose-3-phosphate (G3P), Fig. 15). Here 10 to 12 matrix layers seem to be optimal. For lipids, the situation depends on a compound. For some of them, the trend is similar, while for others is the opposite. To effectively observe lipids and small molecules,12 layers seem to be the most promising. It has to be mentioned that NEDC matrix has the lowest intensity of the three tested matrices in the negative ionization mode with a comparable s/n ratio (Fig. 21).
DAN (2,5 mg/ml 50% ACN – negative ionization mode)
For DAN matrix Z =1 and L = 16 layers gives the highest intensity, and the trend for s/n ratio is the same. Spraying nozzle height at the highest position gives the best results (Fig. 16,17).