Studies in Derivative Chronopotentiometry: II . Analysis of Multicomponent Systems

Abstract

Instrumental compensation for diffusion current of prior steps is investigated for the derivative chronopotentiometry of multicomponent systems. This technique, in combination with the instrumental compensation and mathematical correction for charging current described in a previous paper (1) is applied to the analysis of multicomponent systems by standard addition and titration. As examples, an amount of 0.2 ~moles of cadmium was determined by standard addition in the presence of 100 ~moles of lead and an amount of 2 ~moles of cadmium was titrated with EGTA in the presence of 50 ~moles of copper.Chronopotentiometry of solutions containing two or more electroactive substances which undergo con-* Electrochemical Society Active Member. secutive electrode reactions suffers the inherent disadvantage that the faradaic current for the second and subsequent components is reduced by the amount of the residual diffusion current from the more easily ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 128.122.253.212 Downloaded on 2015-06-22 to IP

Chronopotentiometry with programmed current

“…If the system is irreversible, Equation 16 reduces to can be used to predict the relative values of the transition times for successive reductions taking place in a multicomponent system. As pointed out by Delahay and Mamantov ( 4 ) and by Reilley,Everett,and Johns (6), at the conclusion of the transition time associated with the most easily reduced species, the potential jumps to a more negative value where a second species begins to be reduced, but the oxidized form of the first species continues to diffuse to the electrode and be reduced, so that the impressed current is split between the two components.…”

“…The coordinates of the intermediate minimum are shown (14) to be functionally related to the transition time, and a measurement of this quantity is essentially unaffected by charging current. Sturrock and co-authors (15)(16)(17)(18) have modernized this treatment by providing positive feedback to add to the applied current a signal proportional to the derivative, so that the current impressed upon the system constitutes faradaic current only.…”

“…The Irreversible Case. If the system is irreversible, Equation 16 reduces to L|y[-P/<2p+i>]t(Y)e«(Y)| = 1 -J_Ljl(y)yt-2p/(2P+i)]) (26) s In Table IV are listed values of (21/z -1) for various z corresponding to potentially interesting physical situations. The value for q = p = 0 is identical to that given by the previous authors (4, 6); that for q = 1 /2, p = 0 agrees with the predictions of Murray and Reilley (27) for current varying as the square root of time; the value for q = 1, p = 0 corresponds to Oldham's Equation 53 (24).…”

Fast step-potential pulse chronopotentiometry

“…The performance of an enzyme electrode is ultimately dependent on the ability of its enzymatic membrane to sustain and protect the enzyme. Among the available methods of enzyme immobilization, four methods are currently used: adsorption followed by reticulation with bifunctional reagents such as glutaraldehyde (1), covalent coupling between enzyme and activated support (2)(3)(4)(5) or activated enzyme and support (6)(7)(8), and reversible immunological coupling (9). Those involving covalent coupling to solid supports are of great interest since they generally yield the best activity stabilities (10).…”

“…Nearly a 100% current efficiency was obtained by feeding the residual currrent generated by the second cell to the first cell (5). An alternative instrumental approach involves the use of the first derivative (cLE/dt) value as a readout and as a signal source for the positive feedback loop used to compensate the cell capacitance current (6)(7)(8). This approach combined with a graphical correction was successfully used to measure a very short transition time (millisecond and submillisecond) with a dropping mercury electrode.…”