Observation of gas-phase molecular dications formed from neutral organics in solution via chemical electron-transfer reactions by using electrospray ionization mass spectrometry

AbstractThe first observation of organic dications formed by multiple electron loss in electrospray mass spectra is reported. The dications of β-carotene, canthaxanthine, cobalt(II) octaethylporphyrin, and nickel(II) octaethylporphyrin were created in solution via chemical electron-transfer reactions and detected in the gas phase by electrospray ionization mass spectrometry (ES-MS) using a flow-injection experiment. The analytes were injected into a flowing solvent—oxidant stream (10 μL/min) composed of dried methylene chloride containing ∼ 0.1% by volume trifluoroacetic acid and 0.1% by volume antimony pentafluoride (SbF5). The dications created in this oxidizing solvent system were preserved for detection by rapidly transferring them from the reactive solvent—oxidant system to the gas phase, where, in the absence of the solvent system, they were “long-lived” and amenable to mass analysis. This work demonstrates means to produce ions novel to ES-MS and means to detect and study by ES-MS species that are short-lived in solution. In addition, this work shows that electrospray ionization can potentially be used to generate gas-phase dications for mass spectrometric study that are difficult to produce directly from gas-phase neutrals by other ionization techniques (e.g., M2+ from β-carotene)