Nina F. Zakharchuk

A comparative study of Prussian-Blue-modified graphite paste electrodes and solid graphite electrodes with mechanically immobilized Prussian Blue

Abstract The cyclic voltammetry of Prussian Blue was studied using two different types of electrodes. In one case microcrystalline particles of Prussian Blue were mechanically immobilized on the surface of a paraffin-impregnated solid graphite electrode, whereas in the other the Prussian Blue was added to a paste of graphite and silicone oil. The overall behaviour of Prussian Blue in both electrodes is very similar to the well-known behaviour for electrodes with an electrochemically synthesized Prussian Blue film. Differences were observed for the modified paste electrode, particularly in acid-containing solutions. Prussian Blue exhibits pronounced ion-exchange properties in acid solutions. New voltammetric peaks are observed which are clearly related to an exchange of protons between Prussian Blue and the solution. In mixed solutions containing potassium ions and protons competition between these cations is visible. Scanning electron microscopy in conjunction with energy dispersive X-ray analysis supports a reaction scheme which includes both cations. This study provides evidence for the ability of protons to undergo a chemically reversible intercalation in the Prussian Blue lattice. An additional aim of this study was to assess the reliability of experiments using graphite paste electrodes with an organic binder. The results show that the binder affects the electrochemistry of Prussian Blue, but the similarities between “pure” Prussian Blue and that in the paste electrode are clearly dominant.

Syntheses, Structures, and Electrochemical Properties of Inclusion Compounds of Cucurbit(8)uril with Cobalt(III) and Nickel(II) Complexes

Inclusion compounds of a macrocyclic cavitand cucurbit[8]uril (CB[8]) with cobalt(III) and nickel(II) complexes of 1,3-diaminopropane (tn) and 1,3-diamino-2-propanol (tmOH) { trans-[Co(tn) 2Cl 2]@CB[8]}Cl.14H 2O ( 1), { trans-[Co(tmOH)(tmO)]@CB[8]}Cl 2.22H 2O ( 2), and { trans-[Ni(tmOH) 2]@CB[8]}Cl 2.22H 2O ( 3) were synthesized and characterized by X-ray single crystal analysis, IR spectroscopy, ESI-MS, and by solid-state stripping voltammetry. The encapsulation of trans-[Co(tn) 2Cl 2] (+) within the cavity of CB[8] stabilizes the complex toward ligand substitution reactions in aqueous solution. The electrochemical study demonstrates that CB[8] prefers the oxidized species in trans-[Co(tn) 2Cl 2] (+)/ trans-[Co(tn) 2Cl 2] (0) and trans-[Co(tmO)(tmOH) 2] (2+)/ trans-[Co(tmO)(tmOH) 2] (+) redox couples, but stabilizes the reduced form trans-[Ni(tmOH) 2] (2+) against the oxidized species. The reversibility of voltammogram shapes evidence that for the inclusion compounds 1- 3 electron transfer reactions proceed within the cavity of the host.

Express standardization of sulfide solutions using voltammetric titration on two points

A new method called voltammetric titration on two points for express (≤5 min) standardization of unstable sulfide solutions has been developed. The method can be used as an alternative to the classical K3[Fe(CN)6] titration. The same redox reaction underlies the new method: 2[Fe(CN)6]3− + S2− → 2[Fe(CN)6]4− + S0. The analytical signal, current of ferricyanide reduction, is used for immediate calculation of the sulfide concentration. Two analytical signals of electrochemically active K3[Fe(CN)6] before (I0) and after (I1) its quantitative interaction with the analyzable sample is enough to get an accurate concentration. The method accuracy has been confirmed by comparison of experimental (Δexp) and calculated (Δcalc) data, and with recovery study.