Ronald R. Schroeder

Staircase voltammetry with varied current sampling times: Theory for diffusion controlled, rate controlled, and mixed rate and diffusion controlled electrode reactions

Summary The theory for staircase voltammetry with a varied current sampling time has been derived for the cases of reversible, irreversible, and quasireversible electrode reactions. The equations derived have been used to calculate theoretical voltammograms employing several different values of the electrode reaction parameters k s and α n a and several values of the experimentally controllable step time, step size and current sampling time. The current sampling time is shown to be an important parameter in the application of staircase voltammetry to analytical and kinetic studies.

Potentiometric Ion-, Gas-, and Bio-Selective Membrane Electrodes

Abstract Membrane electrodes are relatively simple electrochemical devices that can be used for the direct measurement of ions, gases, and biomolecules in complex samples. Selectivity for one species over another is determined by the nature and chemical composition of the membranes and associated reaction layers used to fabricate the devices. All membrane electrode probes employ at least one ion-selective membrane as the ultimate transduction element. This indicator membrane serves as an additional component of a classic two-electrode galvanic cell. The potential developed at the membrane/sample interface is directly or indirectly related to the activity or concentration of analyte in the sample. Because cell potentials are detected under essentially zero-current conditions, analytical measurements with these probes are generally not subject to the mass transfer and electron transfer kinetic limitations that often plague voltammetric or amperometric techniques. In this report, we review the current state ...

Application of staircase voltammetry with a varied current sampling time

Summary The technique of staircase voltammetry with a varied current sampling time has been evaluated with regard to its application in electrochemical kinetic studies. Instrumentation for staircase voltammetry and procedures to implement the technique and evaluate the data obtained are described. Experiments involving reactions with known kinetic parameters were used to evaluate the technique itself and the recently derived theory for staircase voltammetry.

A Versatile Signal Generator for Voltammetric Techniques

SUMMARY A signal generator has been designed to produce precise triangular waves and a variety of ramp-and-hold signals. The circuit involves a network of Zener diodes and two conventional operational amplifier circuits. An externally generated ramp voltage is required and can be obtained from either an operational amplifier integrator or the sweep generator from a cathode ray oscilloscope. The ramp-and-hold signals have been proven to be extremely useful in stationary electrode polarography, especially when dealing with multicomponent system and complex reaction mechanisms. Triangular waves with scan periods from about 150 sec to less than 1 msec can be produced and a potential “hold” can be obtained at any desired point.

Electron-transfer kinetics and equilibria of copper(II/I) complexes with 1,4,7-trithiacyclononane. A square scheme mechanism involving ligand addition

The electron-transfer kinetics of copper(II/I) complexes formed with the macrocyclic terdentate ligand 1,4,7-trithiacyclononane ([9]aneS3 = TTCN = L) have been investigated under a variety of conditions. The relevant equilibrium constants, complex formation and dissociation rate constants, and redox potentials in both water and acetonitrile have also been determined. The predominant oxidized species in both solvents is CuIIL2, although the 1 ∶ 1 complex, CuIIL(H2O)3, can become dominant in water at high Cu(II) concentrations. The predominant reduced species is the 1 ∶ 1 complex, CuIL (i.e., CuIL(H2O) or CuIL(CH3CN)), as confirmed by electrospray mass spectrometry, pulsed square-wave voltammetry, cyclic voltammetry and the ligand dependence of the oxidation kinetics. Electron transfer occurs almost exclusively through the bis redox couple, CuII/IL2, even for solutions containing predominantly CuIIL(H2O)3. In the latter case, reduction involves a three-step sequence in which (i) CuIIL(H2O)3 reacts with L to produce CuIIL2, (ii) electron transfer occurs and (iii) L dissociates again to yield CuIL(H2O). The sluggishness of direct electron transfer in the 1 ∶ 1 complex is attributed to the unfavorable energetics of forming or dissociating strong copper–solvent bonds combined with the accompanying re-structuring of the surrounding solvent.