Naslov
Effect of the HEPES buffer on the square-wave voltammetry of the copper(II)-salicylaldoxime complex.

Autori
Cuculić, Vlado ; Branica, Marko

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Skup
J. Heyrovský memorial symposium on advances in polarography and related methods

Mjesto i datum
Prag, Češka Republika, 30.08.2000. - 02.09.2000

Vrsta sudjelovanja
Poster

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
square-wave voltammetry; copper

Sažetak
The effect of the 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) on the square-wave voltammetry (SWV) of the Cu(II)-salicylaldoxime complex were observed by the measurements on a hanging mercury drop electrode (HMDE) and static mercury drop electrode (SMDE). The HEPES, which is very often used as a buffer, is generally accepted as chemically inactive compound. However, it has recently been published that the HEPES enhances electrochemical signal of Co(II), Ni(II), Fe(III) and Cu(II) organic complexes up to four times and the reduction peak potentials shifted to positive values. The reduction mechanism of the Cu(II)-SA complex can be characterized by varying SW frequency (f) and pulse amplitude (a), as well as by separating the resultant currents into the reduction and oxidation components. In the range of the frequencies from 5 to 500 s-1, the reduction current linearly increases in the 0.55 M NaCl and 0.7 M NaClO4 electrolyte solutions. In a 0.55 M NaCl solution, the linear slopes, in the absence and in the presence of HEPES buffer, were found to be 5 and 11.5 mA/100 s-1, respectively. This suggest the reversible redox processes with the reactant adsorption. The reduction current increases linearly with the increase of the pulse amplitude up to 30 mV. The reduction peak widens in the amplitude range between 30 and 100 mV, above which the peak splits in two, what evidently confirms the reversibility of the Cu(II)-SA complex redox process. The addition of HEPES surely affects the electrode process of the Cu(II)-SA complex, since the reduction peak current increases twice in a 0.7 M NaClO4 solution, and the reduction potential shifts towards more positive values (for about 50 mV). These results suggest a mechanism which facilitates an electron transfer between the electrode and the Cu(II)-SA complex in the presence of the HEPES molecules. The facilitated electron transfer possibly includes the reorientation of the Cu(II)-SA molecules adsorbed on mercury surface in the presence of the HEPES buffer which acts as a surfactant. Generally, one can suggest that prior to measurements, the electrolytes containing the so-called "inert" buffers, should be thoroughly tested in order to prevent unexpected effects they might exert upon the electrochemical reactions of the systems investigated, as well as to avoid ambiguous results.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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