Study on the redox reactions for organic dyes and S-nitrosylated peptide in electrospray droplet impact.

Reduction of analytes in ionization processes often obscures the determination of molecular structure. The reduction of analytes is found to take place in various desorption/ionization methods such as fast atom bombardment (FAB), secondary ion mass spectrometry (SIMS), matrix-assisted laser desorption/ionization (MALDI) and desorption ionization on porous silicon (DIOS). To examine the extent of the reduction reactions taking place in electrospray droplet impact (EDI) processes, reduction-sensitive dyes and S-nitrosylated peptide were analyzed by EDI. No reduction was observed for methylene blue. While methyl red has a lower reduction potential than methylene blue, the reduction product ions were detected. For S-nitrosylated peptide, protonated molecule ion M + H and NO-eliminated molecular ion M - NO + H were observed but reduction reactions are largely suppressed in EDI compared with that in MALDI. As such, the analytes examined suffer from little reduction reactions in EDI.