Fig. 22 The mass spectra obtained with NEDC, norharmane, DAN and 9AA matrix.
Considering the performance of different matrices in the negative ionization mode (Fig. 22), norharmane matrix could be rejected since it has low peaks intensity and, as a result, it losses the information from the low MW range (e.g., peaks from fatty acids). NEDC is even worse for low MW peaks, but at least it can provide the ion maps for specific substances like glucose, n-acetyl-aspartic acid, glucose-6-phosphate, glucose-3-phosphate, and glutamic acid. DAN matrix produces higher peaks intensity in a lower mass range and seems to provide more information than 9AA. Additionally, it provides quite high intensities and signal-to-noise ratios. So, we recommended NEDC for particular tasks such as glucose analysis, and DAN for the lipids analysis in negative ionization mode.
Table 1. Summary of sample preparation optimization with the aid of wet-interface matrix deposition device (SunCollect®) for MALDI MSI (L – the number of matrix layers, Z - different spraying nozzle height).