Reciprocal Derivative Chronopotentiometry with Programmed Current: Influence of the Reversibility Angela Molina*, Joaquin Gonzalez and Marien M. Moreno Departamento de QuÌmica FÌsica. Facultad de QuÌmica. Universidad de Murcia. Espinardo, 30100. Murcia, Spain e-mail: amolina@um.es Received: March9, 2001 Final version: May23, 2001 Abstract ThebehaviorofthesystemCd 2 /Cd(Hg)intheabsenceandpresenceofanaliphaticalcoholinnoncomplexingmedia isanalyzedinreciprocalderivativeanddoublederivativechronopotentiometrywithprogrammedcurrent(RDCPand RDDCP, respectively). These electrochemical methods have been compared with derivative and double derivative voltammetry (DVand DDV, respectively). When the above system behaves as non reversible, it is not possible to establish a total analogy between chronopotentiometric and voltammetric responses, contrary to the case of a reversible process. ThepeaksobtainedinRDCParebetterresolvedthanthoseobtainedinDVandthedifferentoperationalprinciplesof RDCP compared to those of DV can reduce its susceptibility to ohmic drop effects. Moreover, RDCP and RDDCP are very versatile in the determination of kinetic parameters of electrode processes since, by varying the current amplitudeand/orthepoweroftime u intheprogrammedcurrent,itiseasytoinfluencethereversibilityoftheprocess. Keywords: Reciprocal derivative chronopotentiometry, Programmed currents, Cadmium reduction, Quasireversible processes 1. Introduction Inapreviousarticlewecomparedtheresponsesobtainedin derivative and differential voltammetric techniques and those corresponding to reciprocal derivative chronopoten- tiometrywithaprogrammedcurrentoftheform I(t)  I 0 t u , with u > 1/2(dt u1/2 /dE E andd 2 t u1/2 /dE 2 E responses) for reversible processes [1]. We demonstrated that it is possibletoestablishatotalanalogybetweenbothpotentio- staticandchronopotentiometricresponses[1,2]. Inthisworkweanalyzetheinfluenceofthereversibility on the response corresponding to reciprocal derivative chronopotentiomentry (RDCP) and reciprocal double de- rivative chronopotentiomentry (RDDCP) with pro- grammedcurrentforwhichthefirst(dt u1=2 N /dE)andsecond (d 2 t u1=2 N /dE 2 ) reciprocal derivatives of the normalized E/ t u1=2 N curves are obtained. We have compared these derivatives with those obtained in derivative voltammetry (DV)anddoublederivativevoltammetry(DDV)(first(dI N / dE)andsecond(d 2 I N /dE 2 )derivativesofthe I N /E curve). Incontrasttowhatoccursforreversibleprocesses,inthe case of quasirreversible and totally irreversible processes, normalized chronopotentiometric and voltammetric re- sponses can never be identical due to the fact that their temporaldependencecannotbeeliminated,asitcanbein reversible processes [1]. However, the dt u1=2 N /dE E (RDCP) and d 2 t u1=2 N /dE 2 E (RDDCP) curves for u=0 present a parallel behavior to that of the first and second derivatives of the normalized I N /E curve, except for the particular case u  0 (constant current, I(t)  I 0 ),forwhich the dt u1=2 N /dE±E curve does not present a peak when a totally irreversible process is analyzed. This behavior enablesustodistinguishatotallyirreversibleprocessfrom anotherquasirreversibleone,althoughtodeterminekinetic parametersofthechargetransferreaction a and k' 0 itwillbe necessary to work with programmed current instead of constant current (i.e., values of u different from zero) for which analytical expressions of the peak height and peak potentialsasfunctionsof a and k' 0 aregiven. TheuseofRDCPwithprogrammedcurrentproposedin thisarticleimprovestheusuallyusedconstantcurrentinthe determinationofthermodynamicandkineticparametersof electrodeprocesses.Thisisbecausethepossibilityofbeing abletochoosedifferentvaluesof u leadstothefollowing, amongothers,advantages: ± Amoresuitableselectionofthetransitiontimesinawider rangeofconcentrationthandoesaconstantcurrent[1]. ± An easy analysis of the reversibility of the process [3] since, a quasirreversible process can be treated as reversible(byincreasingthevalueof u and/ordecreasing the current amplitude I 0 ) or as totally irreversible (by decreasingthevalueof u and/orincreasing I 0 ). ± An immediate distinction between a reversible and a quasirreversible process since the normalized RDCP (dt u1=2 N /dE ± E)andRDDCP(d 2 t u1=2 N /dE 2 )responsesvary with u for quasirreversible and totally irreversible proc- esses, whereas these responses remain independent of u forreversibleones. IfwecompareRDCPwithpotentiostatictechniques,wecan statethat: ± The signal obtained with this technique presents more analyticalandkineticadvantagesthanthosecorrespond- 281 Electroanalysis 2002,14,No.4 ¹WILEY-VCH Verlag GmbH, 69469 Weinheim, Germany, 2002 1040-0397/02/0402-0281 $ 17.50+.50/0