Sensitivity of redox reactions of dyes to variations of conditions created in mass spectrometric experiments

Abstract

Redox behaviour of four imidazophenazine dye derivatives under mass spectrometric conditions of matrix-assisted laser desorption/ionization (MALDI), laser desorption/ionization (LDI) from metal and graphite surface, electrospray, low temperature secondary ion mass spectrometry (LT SIMS) and fast atom bombardment (FAB) was studied and distinctions in the reduction-dependent spectral patterns were analyzed from the point of view of different quantities of protons and electrons available for reduction in different techniques. The reduction products [M + 2H](+*), [M + 3H](+) and M(-*), [M + H](-) were observed in the positive and negative ion modes, respectively, which permitted to suggest independent occurrence of reduction and protonation/deprotonation processes. LDI from graphite substrate was the only technique that allowed us to obtain abundant negative ions of all dye derivatives. The yield of field ionization (FI) or field desorption (FD) mechanism to ion formation under LDI from rough graphite surface has been addressed. The sensitivity of reduction of the dyes to variation of reduction-initiating agents confirms high redox activity of the dyes essential for their functioning in natural and artificial systems.

The use of a silica-based heat sink to “uncouple” the matrix-assisted laser desorption/ionization (MALDI) mechanism

“…58 Soft expansion of the matrix by low-energy secondary electron excitation may be partially blocked by the heat sink. 59 Additional experiments using an electron donor in the Fourier transform ion cyclotron resonance (FTICR) mass spectrometer were conducted that support our conclusion 60 that photoelectrons are also involved in the ionization process. 3,47,61 Therefore, if the MALD process is dominant, and not the heat conduction from the metal to the matrix, then the result may be observed as two contradictory trends.…”

Chemically modified porous silicon for laser desorption/ionization mass spectrometry of ionic dyes

“…The effect of negative deprotonated molecule formation in LDI MS was recently investigated for the imidazophenazine dyes matrix-free ionization. [22] However, neither [MB − H] −• nor [MB − H] +• ions were detected in DIOS mass spectra of methylene blue recorded from all the studied PS platforms. Hence, the surface species of the PS (Si-H groups, silanol groups and/or adsorbed solvent molecules) act as hydrogen sources for the MB + reduction.…”

Electrochemical Aspects of Electrospray and Laser Desorption/Ionization for Mass Spectrometry

“…In-source reductions have also been observed for organic dyes (74,81). Using MALDI, Wada and colleagues (74) analyzed methylene blue, Janus green B, crystal violet, and rhodamine B and found that peaks for [M+1] and [M+2] relative to the [M] peak were significantly increased in comparison to those for theoretical isotopic distribution, demonstrating reduction of (M)H + and (MH)H + .…”