Adsorption enhancement in square wave polarography

Abstract

Lours R A V~L E Y . JOHN A. DALZIEL, and WEE TEE TAN. Can. . I . Chem. 59, 3334 (1981).Reduction peaks in single drop square wave polarography (SDSWP) for metal ions such as Cd(1I) and Pb(I1) in the preience of picolinic acid gave peak currents that can be an order of magnitude or more greater than diffusion-limited peaks. Various studies using techniques such as controlled-potential electrolysis. tast polarography. staircase voltammetry. and SDSWP demonstrated that this enhancement effect was due to the adsorption of metal-picolinate complexes on the electrode surface. Since it provides a detection limit of about 0.2 ppb with ions such as Cd(I1). adsorption enhancement appears to be of use in trace analysis under certain circumstances. Linearity is observed only up to 1 x 10-'.M and any substance capable of adsorption is a potential inte~ferent. LOUIS RAMALEY. JOHN A. DALZIEL et WEE TEE TAN. Can. J. Chem. 59, 3334 (1981). Les pics de reduction dans la polarographie a onde carree sur goutte pendante (POCGP) d'ions metalliques tels le Cd(I1) et le Pb(I1) en presence de I'acide picolinique donnent des courants de pointe qui peuvent plus grands que les pics limites par la diffusion par un ordre de grandeur ou plus. Plusieurs etudes utilisant des techniques comrne I'electrolyse a potentiel controle. la polarographie echantillonnke. la voltamerie i impulsions surimposes d'amplitudes croissantes et la POCGP ont demontre que cet effet d'augmentation est due a I'adsorption des complexes picolinate-metal la surface de I'electrode. Puisqu'elle fournit une limite de detection de 0.2 ppb avec des ions comme le Cd(I1). I'augmentation de l'adsorption apparait utile dans I'analyse des traces dans certaines circonstances. On observe une linearite seulement jusqu'a I x M et toute substance capable d'adsorber pourrait eventuellement interferer.[Traduit par le journal] %ntrsduction (3) but little or no enhancement in measured Complexing reagents are often used to selective-c~~r r e n t .However, techniques that use rapid potenly shift the reduction potentials of metal ions. In a tial sweep rates such as cyclic voltammetry (4) or study of this effect using single drop square wave ~~c i l l o~o l a r o g r a~h~ ( 5 ) -or techniques which empolarography (SDSWP) it was observed that addi-ploy pulse waveforms such as normal (6, 7 ) or tion of common complexing reagents such as citric differential pulse ~olarography (DPP) (8)-produce acid or ethylene diamine to solutions both wave shifts and enhanced currents. In generCd(II) with chloride or sulfate salts as supporting "1. the faster the sweep rate Or the the caused cathodic shifts in the peak meaSUremetlt time after application of the pulse, reduction potential and no change or a decrease in the greater the enhancement. Qualitatively the the peak current. This is the expected behaviour. enhancement is caused by the Presence of excess H~~~~~~, the addition ofpicolinic acid (pyridine-2-electroactive species right at the electrode surface carboxylic acid) caused not only the predicted whi...

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