| This dissertation reports the use of redox magnetohydrodynamics (MHD) to induce solution convection and the use of this convection for analytical chemistry applications. Redox MHD is an attractive method suitable for small volume pumping or mixing in portable devices or in high-throughput analyses because there are no required moving parts, flow direction is easily reversed, and only low voltages are required. An external magnetic field (from an electromagnet or compact, permanent magnets), in combination with the electrochemical oxidation or reduction of a redox species in solution, results in a Lorentz force which acts on current-carrying species in solution and leads to bulk convection. Therefore, enhancements in electrochemical currents are observed in the presence of a magnetic field due to increased mass transport to the electrode. For example, anodic stripping voltammetry peak areas for Pb2+, Cd2+, and Cu2+ were increased by 159 +/- 5% in the presence of a 1.77 T magnetic field, using 100 mM Fe3+ as the redox species. Current enhancements as large as 190% were observed at an array of 100 microm band electrodes using a mixture of oxidized and reduced species (0.3 M K3Fe(CN)6 and 0.3 M K4Fe(CN) 6 in 0.1 M KCl) in a 1.65 T magnetic field. Convection around electrode arrays of various dimensions was investigated by tracking the movement of 10 microm polystyrene beads in a thin layer (<1 mm) of solution above the array, through visualization with a microscope, and flow rates as high as 489 +/- 68 microm/s were observed using a 0.38 T permanent magnet. Redox MHD was used to induce convection in solution volumes as small as 1 nL using microcavity devices with 8 microm depths and 50 microm diameters. Redox MHD was also used for directional pumping through electrode-lined channels. Fluid movement was monitored with colored dyes in solution, and a flow rate of 1.3 mm/min (23 microL/min) was achieved using 0.3 M K3Fe(CN) 6/0.3 M K4Fe(CN)6/0.1 M KCl in a 0.55 T magnetic field. This dissertation also investigates the effects of electrode area, scan rate, redox species concentration, magnetic field strength, and density gradients on redox MHD-induced convection. |
