Nicolae Spătaru

Detection of aniline at boron-doped diamond electrodes with cathodic stripping voltammetry

Boron-doped diamond (BDD) electrodes were used to investigate the possibility of detecting aniline by linear-sweep cathodic stripping voltammetry. It was found that the dimeric species (p-aminodiphenylamine and benzidine) formed by anodic oxidation of aniline during the accumulation period are involved in electrochemically reversible redox processes and, in acidic media, the shape of the stripping voltammetric response is suitable for aniline detection in the micromolar concentration range. The low background current of conductive diamond is an advantage compared to other electrode materials and allows a detection limit of 1muM. Weak adsorption properties and the extreme electrochemical stability are additional advantages of BDD and it was found that, even after long-time measurements, the electrode surface can regain its initial activity by an anodic polarization in the potential region of water decomposition.

Voltammetric detection of phenol at platinum-polytyramine composite electrodes in acidic media.

A composite obtained by depositing platinum nanoparticles in a polytyramine (PTy) matrix, electrochemically formed on graphite substrate, was used as electrode material for the investigation of phenol oxidation by use of anodic voltammetry. The results show that, in acidic media, the measurement of the oxidation peak current can be used as the basis for a simple, rapid method for the determination of phenol within a concentration range of 0.3-10 mM. A much better resistance to fouling during phenol detection (compared both with smooth platinum and with Pt nanoparticles on bare graphite substrate) is the main advantage of the Pt-PTy composite. These results are also noteworthy because they provide a basis for additional experiments devoted to obtaining new composite materials with improved performances for phenol anodic oxidation.

Anodic Deposition of RuO x ∙ nH2O at Conductive Diamond Films and Conductive Diamond Powder for Electrochemical Capacitors

Cyclic voltammetry was used in order to directly deposit hydrous ruthenium oxide (RuO x ·nH 2 O) on conductive diamond substrates. It was found that, at the hydrogen-terminated boron-doped diamond (BDD) surface, the overall deposition process is rather slow compared to the case of metal substrates. Nevertheless, the values estimated for the specific charge and specific capacitance by cyclic voltammetric and chronopotentiometric experiments, respectively, compare favorably to those reported in the literature. Additional advantages of using a BDD support are the excellent stability of the response, the extreme robustness even under severe functioning conditions, and, importantly, negligible substrate effects. It was also observed that RuO x ·nH 2 O deposition at a BDD powder surface greatly enhanced both the specific charge and the specific capacitance. These features strongly recommend the use of conductive diamond powder as a substrate for hydrous ruthenium oxide, particularly in view of possible, electrochemical capacitor applications.

Catalytic hydrogen evolution in cathodic stripping voltammetry on a mercury electrode in the presence of cobalt(II) ion and phenylthiourea or thiourea

The system Co(II)-phenylthiourea (PTU)-borax buffer was investigated by cathodic stripping voltammetry (CSV) at a hanging mercury drop electrode. The results of the voltammetric measurements showed that the presence of both PTU and Co(II) gives rise to a new irreversible peak at about -1.5 V. Based upon our previous results obtained in the study of other sulfur compounds and the sulfide ion itself, the peak was ascribed to the catalytic hydrogen evolution superimposed on the reduction of the coordinated Co(II) ion. The catalyst itself is a Co(II) complex with the sulfide ion produced by the decomposition of the analyte during the deposition step. The influence of PTU and cobalt concentration, accumulation conditions and stripping parameters was investigated and complementary data on thiourea are included. The results showed that the measurement of the catalytic hydrogen evolution peak current can be used as a basis for a simple, accurate and rapid method for the determination of PTU within the concentration range 10-100 nM. The catalytic method is relatively free of interferences and could be a suitable alternative for cases in which the stripping peak due to mercury ion reduction in the accumulated mercury compound is disturbed by some interference.

Catalytic hydrogen evolution in the presence of methylthiohydantoin-glycine and cobalt(II) ion: a study by cathodic stripping voltammetry at a hanging mercury drop electrode.

The carbon-sulfur bond in methylthiohydantoin-glycine (MTH-Gly) is broken during the deposition on the mercury electrode at potentials around -0.1 V versus SCE, giving mercury sulfide which is detected by the characteristic cathodic peak at -0.7 V. If cobalt (II) is also present, the product of the deposition step is a mixture of mercury and cobalt sulfides. During the cathodic scan, the last one is reduced to a transient Co(0) species that catalyses the reduction of hydrogen ion to the hydrogen molecule by a mechanism alike to that emphasized for the Co(II)-sulfide ion system (F.G. Bănică, N. Spătaru, T. Spătaru, Electroanalysis 9 (1997) 1341). This electrode process induces a cathodic peak at -1.4 V that enables the determination of MTH-Gly down to 10(-7) M in the borax buffer at pH 8.5. The possible extension of this method to other classes of organic sulfur compounds is briefly discussed.