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(C6H5)(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 AuI2- as well as I-3(-). The AuI2- 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 (C4H9)(4)NSCN 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.