Electrochemical/Electrospray-Mass Spectrometric Studies of the Oxidation of Iodide and Cyanide at Gold and Platinum Electrodes as well as Gas Phase Multiply-Charged Fullerene C60 Anions.
Type of DegreeDissertation
DepartmentChemistry and Biochemistry
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In this dissertation, we introduce a new spherical thin-layer flow cell to interface electrochemistry with electrospray mass spectrometry. The successful applications of the electrochemistry with electrospray mass spectrometry are reported. A spherical thin-layer flow electrochemical cell, which is characterized by easy access to the working electrode for cleaning and a high conversion efficiency, is de- veloped. The cell has a relatively small dead volume from 5 - 10 µL. Calculated Reynolds (Re) numbers predict that the flow pattern around the working electrode is laminar. Both static cyclic voltammograms and hydrodynamic voltammograms at different scan rates indicate that the cell design meets the requirements of a thin layer flow cell. The multi-step oxidation of iodide and the oxidation of cyanide as well as the stepwise reduction of C60 were studied. It was found that B(C6H5)- 4 is a suitable internal standard for negative-ion stud- ies in acetonitrile. The multi-step oxidation results of iodide demonstrate that the apparatus is capable of these very challenging electrochemistry/electrospray mass spectrometry experiments. With iodide at a platinum electrode, we observe well- behaved oxidation to tri-iodide (I- 3 ). Experiments on iodide at gold electrodes are more complex, showing AuI- 2 as well as I- 3 . The AuI- 2 mass spectrometric ion inten- sity varies in a complex way throughout the applied electrochemical voltage range studied; we propose that this variation involves the adsorption of I- on the gold electrode surface. With cyanide at a platinum electrode, we observe C5N- 5 , which is due to the oxidation of cyanide to cyanogen followed by the stepwise condensation of cyanogen with cyanide. At the gold working electrode, the surface oxidation of the gold to gold cyanide complex is observed. This is due to the high stability constant of the gold cyanide complex in acetonitrile. Gas phase observation of C- 60, C3- 60 and C4- 60 anions generated at platinum elec- trodes and detected by electrochemical/electrospray mass spectrometry is reported. The anions are electrochemically generated from solutions of C60 dissolved in mix- tures of toluene and acetonitrile. The gas phase observation of C3- 60 and C4- 60 , despite the fact that they have negative electron affinities, is a result of a repulsive Coulombic barrier to electron loss. These studies, which demonstrate the gas phase stability of C3- 60 and C4- 60 , illustrate the promise of electrochemical/electrospray mass spectrome- try for the studies of metastable anions.