Electrochemical/electrospray mass spectrometric studies of I ^- and SCN ^- at gold and platinum electrodes: Direct detection of (SCN) ₃ ^-

Results on the electrochemistry of I ^- and SCN ^- at gold and platinum electrodes using an electrochemical cell coupled to an electrospray mass spectrometer are reported. We demonstrate that our apparatus is capable of these very challenging electrochemical/electrospray experiments and that B(C ₆H ₅) ₄ ^- is a suitable internal standard for negative-ion studies in acetonitrile. With I ^- at a platinum electrode, we observe well-behaved oxidation to I ₃ ^-. Experiments on I ^- at gold electrodes are more complex, showing AuI ₂ ^- as well as I ₃ ^-. The AuI ₂ ^- mass spectrometric ion intensity 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. In experiments on SCN ^- from (C ₄H ₉) ₄NSCN at gold electrodes, we observe Au(SCN) ₂ ^-. Finally, at platinum electrodes, we directly observe (SCN) ₃ ^-, a species analogous to I ₃ ^- and (CN) ₃ ^- that has been previously postulated but unverified. This important finding was confirmed by the isotope pattern and demonstrates the stability of the anion.