Desorption/ionization behavior of dye molecules in soft cluster-induced desorption/ionization mass spectrometry

Cationic, neutral, and anionic dyes are investigated with respect to their ionization and desorption behavior when analyzed by means of soft desorption/ionization induced by neutral SO2 clusters (DINeC) in combination with mass spectrometry. All types of dyes were desorbed as intact molecular ions without fragmentation. Whereas cationic dyes are exclusively detected as cations without the counterion, anionic dyes were detected both as anions and as cations, e.g., with two of the counterions being attached to the molecular dye ion. For porphyrins, representing an important class of neutral dyes, the ionization behavior strongly correlates with the functional groups available in the molecule. Furthermore, for sulfonate-substituted anionic dyes, the interaction between the sulfonate groups of the dyes and the OH-groups of additives/substrates was observed to influence the desorption efficiency. Application of the soft desorption technique in terms of studying/differentiating fragmentation processes induced by different stimuli is demonstrated.