Enhancement of Anodic Response for DMSO at Ruthenium Oxide Film Electrodes as a Result of Doping with Iron(III)

The oxidation of dimethyl sulfoxide (DMSO) to dimethyl sulfone (DMSO 2 ) is representative of numerous anodic oxygen‐transfer reactions of organosulfur compounds that suffer from slow kinetics at noble metal electrodes. Anodic voltammetric data for DMSO are examined at various RuO 2 ‐film electrodes prepared by thermal deposition on titanium substrates. The response for DMSO is slightly larger at RuO 2 films prepared in a flame as compared with films prepared in a furnace; however, temperature is more easily controlled in the furnace. Doping of the RuO 2 films with Fe(III) further improves the sensitivity of anodic response for DMSO. Optimal response is obtained at an Fe(III)‐doped RuO 2 ‐film electrode prepared using a deposition solution of 50 mM RuCl 3 and 10 mM FeCl 3 in a 1 : 1 mixture of isopropanol and 12 M HCl at an annealing temperature of 450 °C. The Levich plot ( i vs. ω 1/2 ) and Koutecky‐Levich plot (1/ i vs. 1/ω 1/2 ) of amperometric data for the oxidation of DMSO at an Fe(III)‐doped RuO 2 ‐film electrode configured as a rotated disk are consistent with an anodic response controlled by mass‐transport processes at low rotational velocities. Flow injection data demonstrate that Fe(III)‐doped RuO 2 ‐film electrodes exhibit detection capability for methionine and cysteine in addition to DMSO. Detection limits for 100‐μL injections of the three compounds are ca. 3.2×10 −4  mM, i.e., ca. 32 pmol.