Quasireversible Maximum in Cathodic Stripping Square-Wave Voltammetry

Abstract

Square‐wave voltammetry of the cathodic stripping processes exhibits maximum response for a quasireversible redox reaction. This phenomenon, known as a “quasireversible maximum” is explored for kinetic measurements of this class of redox reactions. The apparent reversibility of a redox reaction, together with the position of the quasireversible maximum, depend on the single complex kinetic parameter K, which is defined through the standard rate constant, diffusion coefficient of the ligand and frequency of the SW signal. Critical values of the kinetic parameter Kmax are theoretically calculated for different values of the transfer coefficient α and amplitudes of the signal. If the frequency which corresponds to the quasireversible maximum is experimentally obtained, the standard rate constant of the investigated redox reaction could be estimated. Standard rate constant can be defined either in units cm s–1, which is the same as for a redox reaction of a dissolved redox couple, or only in s–1, which is typical for a redox reaction of an adsorbed redox couple. This feature shows that cathodic stripping redox reactions are an important class of redox reactions which can be regarded as an intermediate form between the redox processes of adsorbed and dissolved redox couple.

Square‐Wave Voltammetry of Cathodic Stripping Reactions. Diagnostic Criteria, Redox Kinetic Measurements, and Analytical Applications

“…Our proposed mechanisms are compatible with the concept of electrosorption reactions used by the former authors [37]. It should be also noted that a comparative study for measuring the kinetics by square-wave and cyclic voltammetry of similar type of reactions is presented in the work of KomorskyLovric [41].…”

“…The intrinsic properties of Reaction I is the parabolic dependency of the dimensionless net peak current on the kinetic parameter K. Within the quasireversible region, the peak current increases dramatically reaching a maximum value for a certain critical value of the kinetic parameter K max . This property is known as ™quasireversible maximum∫, which was thoroughly examined in our previous study [37]. The quasi-reversible maximum appears as a consequence of the current sampling procedure used in the SW voltammetry.…”

“…Furthermore, care has to be taken by using the quasireversible maximum for estimation of the kinetics of Reaction II). It is generally known that the position of the quasireversible maximum is a function of the signal amplitude and the electron transfer coefficient [37]. In addition, the critical kinetic parameter K max for Reaction II) depends on the concentration parameter obeying the following relationship:…”

“…Applying the same procedure for an amplitude of E sw 40 mV, the value k s 1.66 cm s À1 was assessed. It is worth noting that the precision of the kinetic measurements based on quasireversible maximum involves an error of about 10% [37]. Figure 8 shows the quasireversible maximums of AzaU measured for three different concentrations.…”

Diagnostics of Anodic Stripping Mechanisms under Square-Wave Voltammetry Conditions Using Bismuth Film Substrates

“…31 In agreement with previous findings, the position of the quasireversible maximum depends on particular value of k s , revealing that it can be exploited for estimation of the latter kinetic parameter (k s ) in a simple procedure elaborated in detail in previous studies. 30,31 In the reversible kinetic region, the real net peak current depends linearly on the square-root of the frequency, while the net peak potential shifts linearly with log( f) toward more positive potentials. Alongside to the frequency, the SW amplitude is the second powerful instrumental tool to study the electrode reaction for the purpose of the electrode kinetic measurements, as well as optimization of the response for analytical application.…”