Enhancement of Ionization Efficiency by Electrochemical Reaction Products in On-Line Electrochemistry/Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Abstract

A miniaturized two-electrode electrochemical (EC) cell was developed and was coupled on-line with an electrospray ionization Fourier transform ion cyclotron resonance mass spectrometer (ESI-FTICR MS). Electrochemistry on-line with mass spectrometry, EC/ESI-FTICR MS, of triphenylamine (TPA), which undergoes one-electron oxidation to form a radical cation (TPA •+ ), demonstrates a significant sensitivity enhancement compared to ESI-FTICR MS. The on-line EC cell configuration with a stainless steel ES needle as the working electrode produces the highest sensitivity in EC/ESI-MS. The results provide evidence that, during the ES ionization, electrolytic reactions occur mainly in the ES tip region, as previously predicted. The results demonstrate that ESI-MS signal suppression by tetrabutylammonium perchlorate electrolyte, which can be a problem, is minimized in EC/ESI-MS. TPA •+ dimer tetraphenylbenzidine (TPB) can be detected by EC/ESI-MS, together with TPA •+ , as TPB •+ and TPB 2+ . The high mass resolving power of FTICR MS was exploited to identify TPB 2+ dication in the presence of [TPA •+ -H • ] + ions of the same m/z, from their respective isotopic distributions. The dimer dication TPB 2+ can be detected only in EC/ESI-MS.On-line combination of electrochemistry (EC) and mass spectrometry (MS), EC/MS, is an excellent tool for probing electron-transfer chemistry in solution in close to real time. 1 In most recent developments in EC/MS, several research groups have reported the use of an electrospray ionization (ESI) interface for coupling of electrochemistry to mass spectrometry. 2-10 ESI is a soft ionization method, which operates at atmospheric pressure

The role of copper in cysteine oxidation: study of intra- and inter-molecular reactions in mass spectrometry

“…25,26 Permentier et al have studied the on-line electrochemical oxidation and cleavage of proteins in MS, 17,27 because the electrospray itself can be used directly for oxidation. 21,28,29 Thus, reactions or tagging of biomolecules can be achieved by taking advantage of these properties [30][31][32] and sacrificial electrodes can supply the production of metal ions. [33][34][35] Indeed, in positive mode, the electrode used to supply the spray current is an anode that can electrogenerate metallic ions, such as Zn 2+ or Cu 2+/+ .…”

Expanded use of a battery-powered two-electrode emitter cell for electrospray mass spectrometry

“…The two circuits we used for this controlled-current electrochemistry (CCE)-ES emitter setup provided the ability to monitor the current conditions at each electrode and thereby correlate these conditions with the collected mass spectra. Just as in the case of the previous twoelectrode ES emitter systems reported [14,15] and in the case of our three-electrode emitter cell controlled by a potentiostat, [10,11], this CCE-ES system provides the ability to enhance the oxidation of analytes in positive ion mode. Also, like our potentiostat controlled three-electrode emitter cell, this CCE-ES emitter cell provides the ability to turn off analyte oxidation in positive ion mode or reduction in negative ion mode.…”

“…However, one statement is always true regarding such a two-electrode cell: on either electrode a cathodic current results in reduction and an anodic current results in oxidation. We demonstrated a floated ES emitter system utilizing two-tubular stainless electrodes in the mid-1990s [14] and more recently Brajter-Toth and coworkers [15] discussed a very similar two-tubular electrode emitter cell. In each case, these simple battery-powered cells were used only to either enhance the mass spectral signal level of the molecular ion of analytes that could be ionized (oxidized) by electron-transfer or to follow the reaction path of analytes that could be oxidized in the emitter cell.…”

Unexpected formation of [M]2+ from [M+CuCl+H]2+ ions under CID conditions, where M is a molecule of 3,5-bis(2,2’-bipyridin-4-ylethynyl)benzoic acid or its methyl ester

“…Ions [M] +• can be also formed (under ESI conditions) from compounds with low oxidation potential through their oxidation by capillary voltage [14][15][16]. There are also rare examples of formation of ions [M] 2+ as a result of ESI oxidation process [17][18][19][20][21]. However, to the best of our knowledge, there are no examples of [M] 2+ ions formation from respective metal-M complexes.…”