Determination of concentration of saturated ferrocene in aqueous solution

Abstract

The solubility of ferrocene in aqueous solution is known to be approximately 0.04 mmol/dm 3. The solubility values determined by voltammetry have been overestimated because of adsorption on electrodes. This work deals with discerning diffusion from adsorption by altering not only the voltammetric time scale but also the solvents used. Fast voltammetric responses by differential pulse voltammetry and fast scan voltammetry exhibited adsorption behavior. In contrast, quasi steady-state voltammetry showed the diffusion-control, the current of which seemed to evaluate the saturated concentration accurately. However, the currents in the solution including a small amount of organic solvent were smaller than those in the aqueous solution although the concentrations were identical. Solutions including organic solvents have often been used to obtain calibration curves. Therefore, the concentration evaluated from the calibration curve was estimated to be larger than the true concentration. The current in the organic solvent was explained in terms of the extra solvation energy by supersaturation, which was dissipated to low concentrated domains by diffusion. It was formulated in the form of diffusion coefficients. The true concentration was evaluated to be 0.01 mmol/dm 3 by slow scan voltammetry in the solution without calibration curves.

Electroassisted Incorporation of Ferrocene within Sol–Gel Silica Films to Enhance Electron Transfer

“…This corresponds to an anodic/cathodic peak ratio of 0.72 due to the absence of equal concentrations of the redox couple species (ferrocene/ferrocenium) in the bulk solution. Since neutral ferrocene has low solubility in aqueous solutions (7 µg/mL [31]), it was not added to the bulk aqueous solution.…”

Comment on “Direct Electrochemical Determination of Thermodynamic Factors in Aprotic Binary Electrolytes” [J. Electrochem. Soc., 163, A1254 (2018)]

“…5 However, highly reproducible results for the activity coefficients in aqueous systems exist and are based on numerous sources and measurement techniques. The intrinsic problem with applying the ferrocene cell method to a wellstudied aqueous electrolyte is the very low solubility of ferrocene in water, 6 its interactions with water, 7 as well as its chemical instability in water. 8 While acetyl-ferrocene (AcFc) can be easily dissolved in water, 9 it also is unstable in water and no meaningful measurements could be done with AcFc.…”