Use of Microdevices To Determine the Diffusion Coefficient of Electrochemically Generated Species:  Application to Binary Solvent Mixtures and Micellar Solutions

Abstract

A new approach for the determination of diffusion coefficient, D, of redox species is presented. It is based on the use of a home-constructed twin electrode within a thin-layered cell (TETLC) filled with a solution of electroactive species. Values of D are readily calculated, provided that the time required for the electrochemically generated species (produced at the generator electrode) to reach the collector electrode and the distance between both electrodes are known. Other parameters typically required to calculate D, e.g., concentration of the redox species, area of the electrode, and number of electrons transferred, are not needed. Diffusion coefficients of Fe(CN)(6)(3-), Ru(NH3)(6)(2+), and quinone were determined in water and, for Fe(CN)(6)(4-), in binary mixtures with glycerol. The results obtained were in good agreement with literature values. Aqueous glycerol solutions are microheterogeneous, as shown by the dependence on medium composition of the empirical solvent polarity scale, ET(30), determined by the solvatochromic probe RB. The responses of RB and the electrochemically generated species (Fe(CN)(6)(4-)) to the composition of aqueous glycerol mixtures were found to be remarkably similar. Measurements of D of ferrocene in micellar solutions of the cationic surfactant CTABr were also performed. Values of D for ferrocene and the ferrocenium cation are very different, in agreement with the chemical affinity of both species for the cationic micelle.

Measurement of the diffusion coefficients of [Ru(NH3)6]3+ and [Ru(NH3)6]2+ in aqueous solution using microelectrode double potential step chronoamperometry

“…In aqueous solutions it exhibits reversible redox behaviour, and has been widely used for comparisons between models and experiment in theoretical studies of mass transport [5]. Many literature papers have reported the diffusion coefficient for [Ru(NH 3 ) 6 ] 3+ [1,2,5], although very few have done so for [Ru(NH 3 ) 6 ] 2+ [6,7].…”

Toner and paper‐based fabrication techniques for microfluidic applications

“…5E) has also been reported recently [52]. Generator-collector electrochemical microdevices [53][54][55] and new procedures for flow rate control and sample injection in microfluidic channels [56] are some additional examples of recent publications using tonerbased techniques.…”

Cheap and disposable gold and silver electrodes: Trends in the application of compact discs and digital versatile discs for electroanalytical chemistry

“…Ferreira et al [30] have used the same device to determine the diffusion coefficients of Fe(CN)6 3-, Ru(NH3)6 2+ , and quinone were determined in water and, for Fe(CN)6 4-, in binary mixtures with glycerol. Measurements of the diffusion coefficients of ferrocene in micellar solutions of the cationic surfactant CTABr were also performed.…”