Quantifying the Effects of Not Stirring between Repetitive Chronoamperometric Experiments
By Feldberg, Stephen W.; Ojha, Ruchika & Bond, Alan M.
Published in Analytical Chemistry
2013
Abstract
Electroanalytical protocols executed under quiescent conditions generally require that the analyte medium be stirred (or agitated) between repetitions to ensure reestablishment of identical initial conditions in the vicinity of the electrode surface. The present work examines what happens when experimental conditions preclude stirring. We consider two general schemes: Scheme 1 where the potential is stepped from Estart to Estep to oxidize the initially present reduced redox moiety, A, to B under diffusion control (i.e., [A]x=0 = 0) for 0 ≤ t ≤ τ1 followed by a second potential step from Estep back to Estart and continuing for τ1 < t ≤ τ2 during which time species B is reduced back to the initially present species A under diffusion control (i.e., [B]x=0 = 0) and Scheme 2 where the potential is again stepped from Estart to Estep to oxidize A to B under diffusion control for 0 ≤ t ≤ τ1 followed by a second potential step from Estep back to Estart and continuing for τ1 < t ≤ τ2 during which there is no electron transfer; i.e., the electrochemical conversion of B to A (or vice versa) does not occur, and the electrode is effectively at open circuit for time τ1 < t ≤ τ2. We define a recovery parameter which specifies the concentration of A at distance (DAτ1)1/2 from the electrode as a function of the recovery-time ratio τ2/τ1 and the operative Scheme (J). We show that for any given level of recovery τ2/τ1 for Scheme 2 is much larger than for Scheme 1.