Microwave-enhanced electrochemical processes in micellar surfactant media

High intensity microwave radiation effects are demonstrated for electron transfer processes at 25 or 50-mu m diameter platinum electrodes immersed in micellar sodium dodecylsulfate ( SDS) solutions. First, a solution containing 2 mM Fe(CN)(6)(3-) and 2 mM Fe(CN)(6)(4-) in aqueous 0.1 M NaCl with and without SDS is employed to calibrate the electrode temperature and mass transport conditions. Addition of 0.1 M SDS has only a small effect on the microwave enhanced voltammetry for the Fe(CN6)3-/4- system. Next, two highly water-insoluble redox systems are studied. A solution of 1 mM tert-butylferrocene in aqueous 0.1 M NaCl containing 0.1 M SDS is shown to give no current response in the absence of microwaves. In the presence of focused microwaves at a platinum disc electrode, a strong current for the one electron oxidation of tert-butylferrocene is detected presumably due to localized disruption of the micellar solution. Concentrations of tert-butylferrocene down to the micromolar level are detected. alpha-Tocopherol, a lipophilic vitamin and antioxidant, is soluble in aqueous 0.1 M SDS/0.1 M NaCl. In the presence of microwave radiation, a strong and concentration dependent anodic current response consistent with the two-electron oxidation of alpha-tocopherol is observed. A heptode array of seven individual 50 mu m diameter platinum microelectrodes placed in ca. 720 mu m distance of each other is shown to allow microwave enhanced currents to be increased sevenfold with each electrode exhibiting the same microwave effect.